18th Czech and Slovak Conference on Magnetism

Jul 7, 2025, 12:00 AM → Jul 11, 2025, 2:00 PM Europe/Bratislava

Pavol Sovák (Pavol Jozef Šafárik University in Košice, Faculty of Science, Institute of Physics), Adriana Zeleňáková (Pavol Jozef Šafárik University in Košice, Faculty of Science, Institute of Physics)

Dear Colleagues and Fellow Scientists,

on behalf of Organizing Committee we have the pleasure to announce the 

18^th Czech and Slovak Conference on Magnetism (CSMAG'25)

which will be held 

from July 7^th to 11^th, 2025 

in the beautiful location of the Strbske Pleso in High Tatras, Slovakia. 

The objective of the conference is to offer the opportunity for the Slovak and Czech scientists and guests from other countries working in the field of basic and applied magnetism to present their recent results and to exchange ideas and technical information.

Conference will take place in the lecture halls of congress centre of Hotel Patria. 

Each session comprises both oral (invited and contributed talks) and poster presentations. Invited talks will take 30 min. Contributed talks will have duration of 15 min. The area allocated to each poster will be approximately 1.0 m x 1.2 m. The working language of the conference is English.
 

Mon, July 7

9:00 AM Registration

12:00 PM LUNCH

1:30 PM CSMAG'25 - Opening Address

Invited talks: Opening session

Convener: Jaroslav Fabian (University of Regensburg)

1 Unexpected $1/4$ and $1/2$ Magnetization Plateaus in the Rare-Earth Shastry-Sutherland Ising Magnet Er$_2$Be$_2$GeO$_7$

The Shastry-Sutherland lattice is one of the paradigmatic geometries used in frustrated magnetism, and the properties of the Heisenberg and Ising models on this lattice have been studied extensively over the last two decades. The Heisenberg model has several well identified properties, including a spin gap and a remarkable series of magnetization plateaus at $1/8$, $2/15$, $1/6$, $1/4$, $1/3$, $2/5$ and $1/2$, all observed in an almost perfect realization of that model, SrCu$_2$(BO$_3$)$_2$. In comparison, the Ising model on the same lattice is expected to exhibit simpler physics, with only a $1/3$ plateau, and for a long time no clean experimental realization was known. Recently, a family of rare-earth compounds with Shastry-Sutherland geometry has been synthetized, and one of its members, Er$_2$Be$_2$GeO$_7$, has a magnetization curve typical of an Ising model, with nearly vertical jumps between plateaus [1]. However, quite surprisingly, there are two plateaus at $1/4$ and $1/2$, and no plateau at $1/3$, in clear contradiction with the theoretical expectation. In this talk, I will argue that this very peculiar plateau sequence has its source in a small orthorhombic distortion visible in single-crystal neutron scattering experiment. This distortion induces two different values of the exchange couplings on the dimers of the Shastry-Sutherland lattice, and, thanks to extensive analytical and numerical investigations, we have shown that this is sufficient to replace the $1/3$ plateau by two plateaus at $1/4$ and $1/2$. A complete account of all properties, including specific heat and neutron scattering inside the plateaus, can be achieved if residual farther range dipolar interactions are included. However, without the orthorhombic distortion, the correct plateau structure could not be explained, as revealed by ground state simulations of the dipolar model (J. A. Koziol and K. P. Schmidt, private communication).

Acknowledgements

This work was supported by NSF award number DMR-2327555 (Duke University) and the Swiss National Science Foundation grant number 212082 (EPFL).

References

[1] L. Yadav et al., “Unprecedented Fractional Magnetization Plateaus in a New Shastry-Sutherland Ising Compound,” 2024, arXiv. https://doi.org/10.48550/ARXIV.2405.12405

Speaker: Frédéric Mila (Ecole Polytechnique Fédérale de Lausanne)

2 Induction-Heated Magnetic Nanoparticles for Catalytic Hydrogen Production

Induction-heating of nanoparticles placed inside chemical reactors is an alternative green approach for heating high-temperature endothermic catalytic reactions such as steam methane reforming (SMR) [1,2]. As of today, most of the world's hydrogen is produced from natural gas through SMR, but the reaction has conventionally been heated by firing, causing $\sim 1 \%$ of the world’s CO$_2$ emission.

This talk addresses the potential of induction heating. Magnetic nanoparticles can heat locally "from the inside" of the reactor, supplying heat where it is needed, while avoiding large temperature gradients across the catalyst bed [1,2]. Moreover, the heating can be powered by electricity from renewable sources and may due to faster reactor startup times exploit periods of surplus electricity [1,2].

Our recent work show how CoNi nanoparticles on an alumina support can act both as catalyst and as magnetic susceptor to drive SMR at high methane to hydrogen conversion rate at high temperatures ($\sim 800$ °C) [1,2]. The Co:Ni composition can be tuned for optimal performance at given operating temperatures and induction field amplitudes [1]. Moreover, composition can be chosen such that the Curie temperature prevents overheating [1]. A new sample holder for vibrating sample magnetometry (VSM) enables studies of the powder materials at high temperature in well-controlled gas atmospheres [3].

The talk further discusses the applicability of induction heating of magnetic nanoparticles to drive catalytic reactions [1,2] and compares induction heating with conventional heating and resistive heating [4], in the case of SMR and more generally.

Acknowledgements

The work has been supported by Innovation Fund Denmark.

References

[1] M. R. Almind et al., “Optimized CoNi Nanoparticle Composition for Curie-Temperature-Controlled Induction-Heated Catalysis,” ACS Applied Nano Materials, vol. 4, no. 11. American Chemical Society (ACS), pp. 11537–11544, Oct. 20, 2021. https://doi.org/10.1021/acsanm.1c01941
[2] M. G. Vinum et al., “Dual‐Function Cobalt–Nickel Nanoparticles Tailored for High‐Temperature Induction‐Heated Steam Methane Reforming,” Angewandte Chemie, vol. 130, no. 33. Wiley, pp. 10729–10733, Jul. 13, 2018. https://doi.org/10.1002/ange.201804832
[3] M. R. Almind et al., “Retrofittable plug-flow reactor for in situ high-temperature vibrating sample magnetometry with well-controlled gas atmospheres,” Review of Scientific Instruments, vol. 94, no. 6. AIP Publishing, Jun. 01, 2023. https://doi.org/10.1063/5.0113493
[4] S. T. Wismann et al., “Electrified methane reforming: A compact approach to greener industrial hydrogen production,” Science, vol. 364, no. 6442. American Association for the Advancement of Science (AAAS), pp. 756–759, May 24, 2019. https://doi.org/10.1126/science.aaw8775

Speaker: Cathrine Frandsen (Technical University of Denmark)

3 Investigating Quantum States in Spin Chain Materials

The antiferromagnetic spin-$1/2$ spin chain with Heisenberg-Ising (XXZ) anisotropy is a rich source of novel phenomena. Good physical realizations are the compounds SrCo$_2$V$_2$O$_8$ and BaCo$_2$V$_2$O$_8$ where the Co$^{2+}$ ions have effective spin-$1/2$ and are coupled by antiferromagnetic interactions into chains while collinear long-range magnetic order occurs below $T_N\approx 5$ K due to weak interchain coupling. In a longitudinal magnetic field applied along the easy axis, the magnetic order is suppressed and using inelastic neutron scattering and optical spectroscopy we find the evidence for complex bound states of magnetic excitations, known as Bethe strings. Furthermore, the characteristic energy, scattering intensity and linewidth of the observed string states exhibit excellent agreement with precise Bethe ansatz calculations. Our results confirm the existence of the long-sought Bethe string excitations predicted almost a century ago. Application of transverse magnetic field along the direction perpendicular to the easy axis induces a quantum phase transition where the antiferromagnetic order is destroyed at a three-dimensional quantum critical point. The evolution of the excitations is investigated as a function of field revealing a complex series of modes and continuum scattering which are compared to theory. At a particular field still within the antiferromagnetically ordered phase we find a sequence of excitations whose energies match the predictions based on the E$8$ Lie group symmetry.

Acknowledgements

Funding was provided by Helmholtz Gemeinschaft.

Speaker: Bella Lake (Helmholtz Zentrum Berlin, Germany)

4 High-$T_c$ Cuprates and Murunskite: The Importance of Very Local Interactions

Despite the complexity of high-$T_c$ cuprates, we have identified a series of surprisingly simple and universal behaviors [1-7]. Building on these findings, we show [8,9] that the phenomenology of cuprates across the phase diagram can be fully described by two relatively simple relations:
$\hspace{2cm}$$1 + p = n_{loc} + n_{eff}\;\; (1)\hspace{2cm} \rho_S = n_{eff}\cdot(O_S\,n_{loc})\;\; (2)$
where $p$ is the doping, $n_{eff}$ is the density of Fermi-liquid carriers, $n_{loc}$ is the density of (Mott-like) localized charge, while $\rho_S$ is the superfluid density and $O_S$, is compound-dependent constant fine-tuned by the local crystal structure [9]. Importantly, all terms can be experimentally determined directly.

Murunskite (K$_2$FeCu$_3$S$_4$) can be viewed as a bridging compound between cuprate and iron-pnictide superconductors [10]. It is isostructural to iron-pnictides but, like parent cuprate compounds, it is a $\sim 1$ eV insulator, as determined from optical conductivity. Long-range magnetic order is observed below $97$ K, with a nearly commensurate quarter-zone wave vector, as determined by neutron studies [11]. Mössbauer and XPS measurements reveal that the magnetic transition is accompanied by an orbital transition. Remarkably, full orbital and spin order is achieved at $30$ K, despite the presence of two distinct magnetic Fe sites at higher temperatures, where Fe is randomly distributed among non-magnetic Cu.

We will argue that understanding the role of the localized hole ($O_S$ $n_{loc}$) within the CuO$_2$ unit in cuprates, as well as the very local magnetic interactions in murunskite, is key to understanding these materials—and may provide valuable insights for other functional materials as well.

References

[1] N. Barišić et al., “Evidence for a universal Fermi-liquid scattering rate throughout the phase diagram of the copper-oxide superconductors,” New Journal of Physics, vol. 21, no. 11., p. 113007, 2019. https://doi.org/10.1088/1367-2630/ab4d0f
[2] Y. Li et al., “Hole pocket–driven superconductivity and its universal features in the electron-doped cuprates,” Science Advances, vol. 5, no. 2., 2019. https://doi.org/10.1126/sciadv.aap7349
[3] N. Barišić et al., “Universal sheet resistance and revised phase diagram of the cuprate high-temperature superconductors,” Proceedings of the National Academy of Sciences, vol. 110, no. 30., pp. 12235–12240, 2013. https://doi.org/10.1073/pnas.1301989110
[4] S. I. Mirzaei et al., “Spectroscopic evidence for Fermi liquid-like energy and temperature dependence of the relaxation rate in the pseudogap phase of the cuprates,” Proceedings of the National Academy of Sciences, vol. 110, no. 15., pp. 5774–5778, 2013. https://doi.org/10.1073/pnas.1218846110
[5] M. K. Chan et al., “In-Plane Magnetoresistance Obeys Kohler’s Rule in the Pseudogap Phase of Cuprate Superconductors,” Physical Review Letters, vol. 113, no. 17., 2014. https://doi.org/10.1103/physrevlett.113.177005
[6] P. Popčević et al., “Percolative nature of the direct-current paraconductivity in cuprate superconductors,” npj Quantum Materials, vol. 3, no. 1., 2018. https://doi.org/10.1038/s41535-018-0115-2
[7] C. M. N. Kumar et al., “Characterization of two electronic subsystems in cuprates through optical conductivity,” Physical Review B, vol. 107, no. 14., 2023. https://doi.org/10.1103/physrevb.107.144515
[8] D. Pelc, P. Popčević, M. Požek, M. Greven, and N. Barišić, “Unusual behavior of cuprates explained by heterogeneous charge localization,” Science Advances, vol. 5, no. 1., 2019. https://doi.org/10.1126/sciadv.aau4538
[9] N. Barišić & D. K. Sunko. J Supercond. Nov. Magn. 35, 1781 (2022). doi : 10.1007/s10948-022-06183-y
[10] D.Tolj et. al., Appl. Mater. Today 24, 101096 (2021). doi : 10.1016/j.apmt.2021.101096
[11] D. Tolj et. al., arXiv:2406.17108 (2024). doi : 10.48550/arXiv.2406.17108.

Speaker: Neven Barisic (PMF Zagreb & TU Wein)

4:00 PM Coffee break

Section S4: Magnetic materials and heterostructures for spintronics, topological and quantum magnetic phenomena

Convener: Dr Martin Gmitra (Pavol Jozef Šafárik University in Košice, Faculty of Science, Institute of Physics)

5 Spintronics With $2$D Magnets

The emergence of $2$D materials has transformed solid-state physics. The key factor driving research into $2$D materials is the ability to efficiently control the atomic-scale physical properties of monolayers and their heterostructures, which involve weak yet important van der Waals interactions. Spintronics aims to utilize the spin of conduction electrons to develop devices like spin transistors and tunneling junctions. Since the early experiments in graphene, spintronics has advanced, establishing a solid understanding of spin physics in monolayers. Current research focuses on van der Waals heterostructures, which serve as tailored platforms to explore new spintronic phenomena. Tuning electron spin properties in these structures mainly relies on the proximity effect. For instance, ferromagnetic graphene can be created by stacking it with $2$D ferromagnetic semiconductors. Additionally, such spin properties of graphene's itinerant electrons can be tuned through methods like gating and twisting. By combining ferromagnets with strong spin-orbit materials, unique structures can be created that allow for tunable spin interactions. In this talk, I will discuss the recent advances in spin proximity phenomena, but also potential applications related to spin-charge conversion and spin-orbit torques.

Acknowledgements

Funding from CRC1277, EU 2DSPIN-TECH, and SPP2244 is acknowledged.

Speaker: Jaroslav Fabian (University of Regensburg)

6 Computational Study of $1$T-TaSSe Monolayer: A Janus Structure Exhibiting Charge Density Wave Ordering

Janus monolayers of transition metal dichalcogenides (TMDs) constitute a highly interesting group of modern $2$D materials, due to the in-built symmetry breaking and its non-trivial consequences [1]. Among various TMDs, the structures forming charge density waves (CDWs) at low temperatures offer highly complex physics.

In the paper, we report a computational, density functional theory-based study of the properties of a Janus TaSSe TMD monolayer in its $1$T polymorph [2]. The study involves both normal and CDW state with $\sqrt{13}\times\sqrt{13}$ reconstruction, as the parent monolayer compounds (TaS$_2$ and TaSe$_2$) are known to develop such ordering. We provide an extensive comparison of the predicted structural and electronic properties of our Janus system to those of its parent compounds.

For the normal state, we predict the emergence of an electric dipole moment due to the symmetry breaking, with pronounced sensitivity to the perpendicular electric field applied to the structure. The presence of the temperature-dependent imaginary phonon modes marks the instability which is characteristic of the CDW-forming systems.

For the CDW state, a peculiar feature of the electronic structure is the presence of a pair of weakly dispersive bands at the Fermi level. Their splitting stems from the symmetry breaking in Janus structure, yielding the presence of spin-orbit coupling (SOC) characterized by the contribution of both linear and cubic terms [3]. We discuss the possibility of controlling the SOC with the external electric field. Moreover, we address computationally the problem of magnetism in CDW state of our system.

In the field of modern spintronics, heterostructures of CDW-forming TMD with graphene exhibit the unique functionalities [4]. Therefore, we supplement our study with a discussion of the electronic properties of heterostructures composed of monolayer TaSSe and monolayer graphene.

The results suggest the novel interesting platform for studies of CDW-related phenomena.

Acknowledgements

We acknowledge Polish high-performance computing infrastructure PLGrid for providing computer facilities and support within computational grant no. PLG/2024/017470.

References

[1] A.-Y. Lu et al., “Janus monolayers of transition metal dichalcogenides,” Nature Nanotechnology, vol. 12, no. 8. Springer Science and Business Media LLC, pp. 744–749, May 15, 2017. https://doi.org/10.1038/nnano.2017.100
[2] K. Szałowski, “Janus Monolayer of 1T-TaSSe: A Computational Study,” Materials, vol. 17, no. 18. MDPI AG, p. 4591, Sep. 19, 2024. https://doi.org/10.3390/ma17184591
[3] C. Cheng et al., “Nonlinear Rashba spin splitting in transition metal dichalcogenide monolayers,” Nanoscale, vol. 8, no. 41. Royal Society of Chemistry (RSC), pp. 17854–17860, 2016. https://doi.org/10.1039/c6nr04235j
[4] K. Szałowski et al., “Spin–orbit and exchange proximity couplings in graphene/1T-TaS2 heterostructure triggered by a charge density wave,” 2D Materials, vol. 10, no. 2. IOP Publishing, p. 025013, Feb. 23, 2023. https://doi.org/10.1088/2053-1583/acbb19

Speaker: Karol Szalowski (Department of Solid State Physics, Faculty of Physics and Applied Informatics, University of Łódź)

7 High Spin Polarization in Co$_2$FeSn Heusler Nanowires for Spintronics

Spin transfer electronics (spintronics) promises an outstanding improvement of basic electronic devices by incorporating the electron’s spin degree of freedom instead of (or in addition to) their charge. Spin polarized Heusler alloys are highly relevant for spintronic applications owning to their predicted half-metallicity, high Curie temperature and high magnetic moment.

Cylindrical nanowires made of Co$_2$FeSn Heusler alloy with high spin polarization have been synthetized via template-assisted electrochemical deposition in nanoporous anodic alumina membranes. The basic structural and magnetic characterization revealed a B$2$-type cubic ordered Heusler structure and the $[110]$ direction preferably aligned with the longitudinal axis of the polycrystalline nanowires. The easy magnetization axis is parallel to the nanowire´s axis too. Spin polarization measurements using Point-Contact Andreev Reflection spectroscopy between a superconducting Nb tip and Co$_2$FeSn Heusler nanowires have been performed. The spectroscopic measurements performed on the nanowire´s fresh surface released high polarization values i.e. $P = 0.85-1$ and prove that the high spin polarization or half-metallicity will be preserved in the nanoscale regime. The presented results open the possibilities towards future exploration of Heusler nanowires with high spin polarization, which are promising materials for applications in spintronics and high-density magnetic data recording.

Speaker: Mr Pavol Szabo (Centre of Low Temperature Physics, IEP Slovak Academy of Sciences)

8 Low Temperature Magnetic Phase Coexistence in Ni-Fe Layered Double Hydroxides

Layered double hydroxides (LDH) belong to the family of anionic clays which are promising for such applications as water treatment, drug delivery and sensing. LDH are composed of the mixed metal layers where metal cations are surrounded by the edge-linked hydroxide octahedra [1]. The present study is focused on the low-temperature static and dynamic magnetic properties of the Ni$^{2+}_n$Fe$^{3+}$ LDH with the nickel-to-iron ratio ($n$) of $2$ and $3$ in magnetic fields up to $90$ kOe.

In all the Ni$_n$Fe LDH studied, the spontaneous magnetization appears below $17$ K which is accompanied by magnetization loops of a ferromagnetic type. Their peak of the temperature-dependent magnetic susceptibility in the vicinity of $17$ K correlates with the heat capacity anomaly in the same temperature range. The ac magnetic susceptibility peak is frequency-independent, which indicates that low-temperature magnetic behaviour of Ni$_n$Fe LDH may be associated with their long-range magnetic ordering. Upon cooling below about $5$ K, the magnetic behaviour of LDH with the different nickel-to-iron ratio is strongly different. All the Ni$_2$Fe LDH studied demonstrate a step like initial magnetization curve accompanied by the wasp-waisted magnetization hysteresis loop, while no such effect is seen for the LDH with $n = 3$. The effect found suggests that at least two magnetic phases coexist in Ni$_2$Fe LDH at low temperatures. The effect is most likely related to the cluster structure of layers for Ni$_2$Fe LDH which agrees with the experimentally found clustering in Ni-Fe LDH by using Mössbauer spectroscopy [2]. One possible scenario is as follows. Long range magnetic ordering below $17$ K occurs not in the entire layer, but in separate regions, clusters. Below about $5$ K temperature long range magnetic ordering occurs in the inter cluster space. Thus, at low temperatures two magnetic phases with different coercive field values are coexistent and negatively coupled. For a deeper exploration of this phenomenon, X-ray Absorption Spectroscopy (XAS) and Magnetic Circular Dichroism (XMCD) techniques have been applied. The respective studies are in progress.

Speaker: Dr Olena Fertman (B. Verkin Institute for Low Temp. Physics & Eng. of NASU, 61103 Kharkiv, Ukraine)

9 Simulations of Magnetic Scattering at Nano-Scale in Transmission Electron Microscopy

Transmission electron microscopes (TEMs) are versatile instruments providing a wealth of information about materials, such as their elemental composition, local crystal structure, defects or strains and more. Electrons as moving charged particles are also influenced by magnetism in the samples, however, this interaction is typically $3-4$ orders of magnitude weaker than the interaction of electrons with the charge distribution in the sample.

In the last approximately two decades, the microscope hardware went through enormous improvements. Notably, in the context of this work, direct electron detectors have vastly improved the signal to noise ratios in the measurements [1]. Consequently, measuring effects of the atomic scale distribution of magnetic fields in the sample on the scattering of electron beam is becoming more feasible. Recently, experiments using differential phase contrast imaging detected atomic scale magnetic fields [2] and holographic experiments reached atomic scale detection of magnetic fields using a high-voltage microscope [3].

The most commonly used method in simulations of elastic electron scattering in TEMs is so called multislice method [4]. However, this method doesn’t include effects of magnetic fields on the electron beam. We have extended the multislice method to include these effects starting from Pauli equation [5]. We have used this method to simulate magnetic differential phase contrast imaging [6,7] and recently even scattering on magnons [8].

Acknowledgements

We acknowledge financial support of the Swedish Research Council, the Olle Engkvist’s Foundation, and the Knut and Alice Wallenberg Foundation.

References

[1] B. D. A. Levin, “Direct detectors and their applications in electron microscopy for materials science,” Journal of Physics: Materials, vol. 4, no. 4. IOP Publishing, p. 042005, Jul. 28, 2021. https://doi.org/10.1088/2515-7639/ac0ff9
[2] Y. Kohno et al., “Real-space visualization of intrinsic magnetic fields of an antiferromagnet,” Nature, vol. 602, no. 7896. Springer Science and Business Media LLC, pp. 234–239, Feb. 09, 2022. https://doi.org/10.1038/s41586-021-04254-z
[3] T. Tanigaki et al., “Electron holography observation of individual ferrimagnetic lattice planes,” Nature, vol. 631, no. 8021. Springer Science and Business Media LLC, pp. 521–525, Jul. 03, 2024. https://doi.org/10.1038/s41586-024-07673-w
[4] J. M. Cowley and A. F. Moodie, “The scattering of electrons by atoms and crystals. I. A new theoretical approach,” Acta Crystallographica, vol. 10, no. 10. International Union of Crystallography (IUCr), pp. 609–619, Oct. 01, 1957. https://doi.org/10.1107/s0365110x57002194
[5] A. Edström et al., “Elastic Scattering of Electron Vortex Beams in Magnetic Matter,” Physical Review Letters, vol. 116, no. 12. American Physical Society (APS), Mar. 24, 2016. https://doi.org/10.1103/physrevlett.116.127203
[6] A. Edström et al., “Quantum mechanical treatment of atomic-resolution differential phase contrast imaging of magnetic materials,” Physical Review B, vol. 99, no. 17. American Physical Society (APS), May 28, 2019. https://doi.org/10.1103/physrevb.99.174428
[7] F. Krizek et al., “Atomically sharp domain walls in an antiferromagnet,” Science Advances, vol. 8, no. 13. American Association for the Advancement of Science (AAAS), Apr. 2022. https://doi.org/10.1126/sciadv.abn3535
[8] J. Á. Castellanos-Reyes et al., “Dynamical Theory of Angle-Resolved Electron Energy Loss and Gain Spectroscopies of Phonons and Magnons in Transmission Electron Microscopy Including Multiple Scattering Effects,” Physical Review Letters, vol. 134, no. 3. American Physical Society (APS), Jan. 22, 2025. https://doi.org/10.1103/physrevlett.134.036402

Speaker: Jan Rusz (Department of Physics and Astronomy, Uppsala University)

10 The Effect of Magnetization Direction and Stacking of Layers on Charge to Spin Conversion in Graphene on $1$T-TaS$_2$

Heterostructures of transition metal dichalcogenides and graphene provide vast utilization in proposals of novel platform devices [1] benefiting from the proximity-induced effects [2]. Monolayer $1$T-TaS$_2$ is a peculiar example as it is known for its low-temperature magnetism and charge density phase (CDW). The CDW arises as a spontaneous distortion in $1$T-TaS$_2$, forming the David star patterns [3]. The correlated state alters the electronic states of the proximitized graphene [4]. Focusing on the p$_z$ states of graphene, these effects can be captured within a tight-binding model, providing an insight into underlying proximity mechanisms.

Using the Kubo formalism, we study charge to spin interconversion effects in a $1$T-TaS$_2$/graphene heterostructure within the linear response regime. We investigate the impact of the magnetization direction in $1$T-TaS$_2$ on charge to spin interconversion efficiencies. Additionally, we explore different configurations of individual layers and identify the role of the tight-binding parameters in determining the ratio between the Rashba-Edelstein (REE) and the unconventional Rashba-Edelstein effect (UREE).

The (U)REE exhibits a non-trivial dependence on a chemical potential and is proportional to spin accumulation in the (parallel) perpendicular direction relative to the externally applied electric current. It is shown that the Rashba interaction plays a crucial role in the determination of charge to spin conversion coefficients, while the magnetization induces a relative shift of the Dirac cones manifesting in the additional non-analytical behaviour. Furthermore, the different stacking of $1$T-TaS$_2$ and graphene affects the Rashba phase, allowing a switch between UREE and REE.

Acknowledgements

This work has been funded by the EU NextGenerationEU through the Recovery and Resilience Plan for Slovakia under the project No. 09I03-03-V05-00008.

References

[1] J. Azadmanjiri et al., “Graphene-Supported 2D transition metal dichalcogenide van der waals heterostructures,” Applied Materials Today, vol. 19. Elsevier BV, p. 100600, Jun. 2020. https://doi.org/10.1016/j.apmt.2020.100600
[2] M. Gmitra and J. Fabian, “Proximity Effects in Bilayer Graphene on Monolayer WSe$_2$: Field-Effect Spin Valley Locking, Spin-Orbit Valve, and Spin Transistor,” Physical Review Letters, vol. 119, no. 14. American Physical Society (APS), Oct. 04, 2017. https://doi.org/10.1103/physrevlett.119.146401
[3] D. C. Miller et al., “Charge density wave states in tantalum dichalcogenides,” Physical Review B, vol. 97, no. 4. American Physical Society (APS), Jan. 17, 2018. https://doi.org/10.1103/physrevb.97.045133
[4] K. Szałowski et al., “Spin–orbit and exchange proximity couplings in graphene/1T-TaS2 heterostructure triggered by a charge density wave,” 2D Materials, vol. 10, no. 2. IOP Publishing, p. 025013, Feb. 23, 2023. https://doi.org/10.1088/2053-1583/acbb19

Speaker: Juraj Mnich (Pavol Jozef Šafárik University in Košice, Faculty of Science, Institute of Physics)

11 Lattice and Magnetic Excitations in Vanadium van der Waals Trihalides

Two-dimensional (2D) van der Waals (vdW) magnetic materials have gained much attention because of their fundamental properties and notable potential applications in spintronics and data storage

We will present the results of our research on complex magnetic excitations in vdW vanadium trihalides VX$_3$. Particularly, vanadium triiodide VI$_3$ is a peculiar example because it hosts a unique ferromagnetic (FM) order with tilted magnetic moments and a significant unquenched orbital moment on two V sites with different orbital occupations [1]. Moreover, the bulk VI$_3$ is trimorphous [2]. Our study used the complementarity of the infrared (IR) and Raman spectroscopies and density functional theory calculations (DFT) to probe lattice and magnetic excitations. We found clear signatures of the structural transition in the IR spectra at $79$ K, and enhanced variations of phonon frequencies observed near the FM phase onset temperature $\sim 50$ K indicate the strong magneto-elastic coupling. Below Curie temperature, two Raman active modes appear, showing significant softening in the narrow interval around the second structural transition $\sim 30$ K associated with the magnetic structure modification. Below this transition, a highly energetic FM resonance in a terahertz (THz) range shows up. The observed THz FM resonance in VI$_3$ is a promising indicator of the application potential of $2$D vdW FM in ultrafast THz spintronics, even though it was previously considered an exclusive domain of antiferromagnets [3]. Similarly, we have detected the orbital moment also on V-sites in antiferromagnetic counterparts VBr$_3$ [4] and VCl$_3$ accompanied by low-temperature zero-field split antiferromagnetic magnons suggesting a biaxial anisotropy of these materials.

Acknowledgments

This work is a part of the research project GACR 25-15448S, financed by the Czech Science Foundation. Some experiments were performed in MGML (mgml.eu) (project no. LM2023065).

References

[1] D. Hovančík et al., “Large Orbital Magnetic Moment in VI3,” Nano Letters, vol. 23, no. 4. American Chemical Society (ACS), pp. 1175–1180, Feb. 01, 2023. https://doi.org/10.1021/acs.nanolett.2c04045
[2] P. Doležal et al.,"Crystal structures and phase transitions of the van der Waals ferromagnet V⁢I$_3$," Physical Review Materials, vol. 3, no. 12. American Physical Society (APS), Dec. 19, 2019. https://doi.org/10.1103/physrevmaterials.3.121401
[3] D. Hovančík et al., “Terahertz Magnetic and Lattice Excitations in van der Waals Ferromagnet VI3,” The Journal of Physical Chemistry Letters, vol. 13, no. 48. American Chemical Society (ACS), pp. 11095–11104, Nov. 23, 2022. https://doi.org/10.1021/acs.jpclett.2c02944
[4] D. Hovančík et al.,"Robust intralayer antiferromagnetism and tricriticality in the van der Waals compound VBr$_3$," Physical Review B, vol. 108, no. 10. American Physical Society (APS), Sep. 21, 2023. https://doi.org/10.1103/physrevb.108.104416

Speaker: Jiří Pospíšil (Charles University, Faculty of Mathematics and Physics)

7:00 PM WELCOME DINNER

Tue, July 8

Section S5: Fine particles magnetism

Convener: Cathrine Frandsen (Technical University of Denmark)

12 Interplay Between Intra- and Interparticle Effects in Bi-Magnetic Core/Shell Nanoarchitectures

Magnetic nanoparticles exhibit distinctive properties governed by nanoscale effects, making them uniquely suitable for advanced technological and biomedical applications [1]. Among various designs, core/shell nanoparticles composed of spinel ferrites stand out due to their tunable magnetic responses arising from the interplay of intra- and interparticle effects [2, 3].

In this talk, we highlight specific examples of bi-magnetic core/shell nanoparticles, particularly cobalt ferrite (CoFe$_2$O$_4$, CFO) and nickel ferrite (NiFe$_2$O$_4$, NFO) in both direct (CFO/NFO) and inverse (NFO/CFO) configurations. Systematic variation of the shell thickness and particle architecture significantly affects magnetic properties (i.e., magnetic anisotropy, saturation magnetization, and magnetization dynamics). Observed effects cannot be fully described by simple additive models, pointing to a complex interaction between magnetic intraparticle (proximity effect) and interparticle interactions. Experimental insights obtained using remanent magnetization analyses ($\Delta m$-plot) and supported by Monte Carlo simulations allow us to unravel this intricate interplay, underscoring the importance of nanoscale architecture [2, 3].

Our findings emphasize the importance of nanoarchitecture in precisely tuning magnetic behaviors and suggest potential for designing materials with targeted magnetic properties. We also discuss several critical open questions: the mechanisms through which intraparticle and interparticle interactions influence each other; the distinct roles of dipolar and exchange interparticle interactions; the impact of core/shell nanoparticle architecture, including core and shell materials, layer dimensions, and shape; and how these interactions can be harnessed for designing materials with tailored magnetic properties. These examples highlight the broader possibilities awaiting discovery and optimization for applications in data storage, sensors, and biomedical devices.

Acknowledgements

This work was partially supported by the European Commission PathFinder Open programme under grant agreement no. 101046909 (REMAP, REusable MAsk Patterning) funded by the European Union. This work was partially supported byMinestro dell’Universita edella Ricerca, program ERANET Cofund ERA-MIN3, project Rendering 3D (No. JTC-2021_207).

References

[1] A. López-Ortega, et al., “Applications of exchange coupled bi-magnetic hard/soft and soft/hard magnetic core/shell nanoparticles,” Physics Reports, vol. 553. Elsevier BV, pp. 1–32, Feb. 2015. https://doi.org/10.1016/j.physrep.2014.09.007
[2] A. Omelyanchik et al., “Interplay between inter- and intraparticle interactions in bi-magnetic core/shell nanoparticles,” Nanoscale Advances, vol. 3, no. 24. Royal Society of Chemistry (RSC), pp. 6912–6924, 2021. https://doi.org/10.1039/d1na00312g
[3] A. Omelyanchik et al., “Magnetic Anisotropy and Interactions in Hard/Soft Core/Shell Nanoarchitectures: The Role of Shell Thickness,” Chemistry of Materials. American Chemical Society (ACS), Aug. 12, 2024. https://doi.org/10.1021/acs.chemmater.4c01421

Speaker: Prof. Davide Peddis (Department of Chemistry and Industrial Chemistry & INSTM RU, nM2-Lab, University of Genoa)

13 Interplay Between Local Structure and Magnetism of Oxide Nanoparticles

The interplay of structural disorder and magnetism in oxide nanoparticles is a fascinating subject of recent interest. The present work reviews magnetic properties of nanoscale magnetoceramics with a variety of structure types (cubic spinel, perovskite, hexagonal structure, double perovskite). The case studies are presented, focusing on recent progress in a fundamental understanding of the structural disorder–magnetism relationships in complex oxide nanoparticles. The far-from-equilibrium structural disorder in iron containing magnetic nanomaterials is studied by means of $^{57}$Fe Mössbauer nuclear probe spectroscopy. The functional behavior of oxide nanoparticles is characterized by SQUID measurements. It is demonstrated that local structural disorder in the nanooxides may result either in an enhancement of magnetic behavior or in its degradation, i.e., in a desired or undesired magnetic property modification, when compared to magnetism of their bulk counterparts.

Acknowledgements

The present work is supported by the Deutsche Forschungsgemeinschaft (project SE 1407/4-2).

Speaker: Vladimír Šepelák (Karlsruhe Institute of Technology)

14 Silica Coated Zn-Substituted Magnetite Nanoparticles - Biocompatible Contrast Agents for Theranostics

Magnetic nanoparticles of magnetite and its substituted variants, including functional derivatives, show promising capabilities in emerging diagnostic imaging methods and novel therapeutic interventions. In addition to the rapid development of synthesis and functionalization methods, a comprehensive understanding of their fundamental physical characteristics and the complex link among composition, microstructure, magnetic properties, and relaxation characteristics is pivotal for the rational design of well-defined magnetic nanoparticle systems. The magnetic behaviour of nanoparticles deviates from bulk materials not only due to finite-size and surface effects but also by the occurrence of metastable states, such as non-equilibrium cation distribution. This study aims to explore the impact of cation distribution on the magnetic properties of Zn$_x$Fe$_{3-x}$O$_4$ nanoparticles, paving the way for their potential applications in theranostics.

The nanoparticles with varying Zn concentrations ($x = 0$, $0.05$, $0.33$, and $0.36$ according to X-ray fluorescence) were prepared using controlled two-step thermal decomposition at relatively low temperature. Their morphology and size distribution were analysed via transmission electron microscopy, revealing log-normal distributions with mean diameters ranging from $5.1$ nm to $14.4$ nm. X-ray diffraction confirmed the spinel structure for all samples. EXAFS was employed to analyse the local environment of Zn and Fe atoms. Local probe methods, solid-state NMR spectroscopy and Mössbauer spectroscopy, along with DC magnetic measurements, provided insights into the distribution of Zn and Fe cations over the tetrahedral (A) and octahedral [B] sites that significantly influences the predominant A-B magnetic interactions, causing changes in the magnetic structure.

High specific surface area of nanoparticles allows quick oxidation during synthesis, yielding mixed maghemite/magnetite composition. The surfactants used during synthesis stabilized the magnetite nanoparticles for prolonged periods, as evidenced by differences in MS spectra between as-prepared and purified samples. Even smallest concentration of Zn substitution was found to suppress the Verwey transition, a well-known effect in magnetite characterized by a dramatic change in structural, electronic, and magnetic properties around $120$ K. The presence of Zn atoms in the structure led to an overall increase of saturated magnetization and transversal relaxivity, with highest observed value slightly higher than those previously reported for other contrast agents with iron oxide cores.

Acknowledgements

The work is supported by Operational Programme Johannes Amos Comenius (FerrMion, CZ.02.01.01/00/22_008/0004591).

Speaker: Dr Denisa Kubániová (Faculty of Mathematics and Physics, Charles University, V Holešovičkách 2, 180 00 Prague, Czech Republic; Institute of Physics CAS, Cukrovarnická 10/112, 162 00 Prague, Czech Republic)

15 Interparticle interaction in nanoparticles and biomedical applications

Superparamagnetic iron oxide nanoparticles (SPIONs), particularly Fe$_3$O$_4$, are among the most extensively studied magnetic nanoparticles (MNPs) due to their high biocompatibility and biodegradability, making them highly suitable for biomedical applications such as magnetic resonance imaging (MRI). While SPIONs have demonstrated promising heating capabilities in magnetic hyperthermia, particularly in prostate cancer therapy, their magnetic response under specific conditions—such as varying distances from an external magnetic field, concentration in tumor tissue, and stability in physiological environments—may not always be optimal [1]. To enhance their performance and adapt them to specific biomedical applications, various modification strategies have been explored.

One of the most effective modification approaches involves altering the chemical composition through cation substitution. Partial replacement of Fe atoms with elements such as Mn, Co, or Ni leads to the formation of spinel ferrites with tunable physicochemical properties. By adjusting the cation distribution within the spinel sublattices, the magnetic characteristics of these nanosystems can be fine-tuned through super-exchange interactions. In addition to compositional modifications, strategies such as controlling nanoparticle shape, size, and surface properties further enhance their magnetic performance. These modifications significantly affect key magnetic parameters, particularly anisotropy and coercivity, which are crucial for improving hyperthermia efficiency.

CoFe$_2$O$_4$ nanocubes in three different size modifications ($10$, $13$, and $17$ nm) were prepared by thermal decomposition and investigated to analyze the impact of size variation on their magnetic properties. SQUID magnetometry was used to examine the magnetic properties of the systems by measuring $M$(H) and $M$(T) curves in both Zero-Field Cooling (ZFC) and Field Cooling (FC) regime. The collected data were then analyzed using appropriate models to investigate the overall magnetic behavior of the systems. From this analysis, values for anisotropy, coercivity, and saturation magnetization were extracted. The results were evaluated for the potential use of these nanoparticles in magnetic hyperthermia. In addition to magnetic properties, the structure of the MNPs was examined using TEM/SEM microscopy, and XRD analysis. Based on the obtained results, these systems show promising potential for application in magnetic hyperthermia.

Acknowledgements

Funded by the EU NextGenerationEU through the Recovery and Resilience Plan for Slovakia under the project No. 09I03-03-V04-00177 and supported by the Slovak Research Agency under the contracts: APVV-20-0512 and VEGA1/047/25.

References

[1] C. Caizer, “Magnetic/Superparamagnetic Hyperthermia as an Effective Noninvasive Alternative Method for Therapy of Malignant Tumors,” Nanotheranostics. Springer International Publishing, pp. 297–335, 2019. https://doi.org/10.1007/978-3-030-29768-8_14

Speaker: Dr Adriana Zeleňáková (Pavol Jozef Šafárik University in Košice, Faculty of Science, Institute of Physics)

10:30 AM Coffee break

Section S1: Theoretical challenges in magnetically ordered and disordered systems

Convener: Jan Rusz (Department of Physics and Astronomy, Uppsala University)

16 Altermagnetism, Antialtermagnetism and Spin Symmetries

Since the 1930s, magnetism has been classified into two main branches: ferromagnetism and antiferromagnetism. Recently, we have identified a third fundamental branch: altermagnetism (see Figure). Altermagnetism exhibits a compensated d-, g-, or i-wave alternating spin order and is found in a wide range of materials, from metals to insulators [1]. This discovery emerged from our systematic classification of spin symmetries [1], analogous to the well-established frameworks used in superconductivity, superfluidity, and the Standard Model.

In this talk, we will outline our decade-long journey leading to the discovery of altermagnets, including the prediction and experimental observation of the anomalous Hall effect and unconventional electronic structure in compensated collinear magnets [2]. We will also present our systematic classification, which-beyond even partial-wave altermag-nets recently revealed a new class of odd partial-wave magnets, termed antialtermagnets [3]. Furthermore, we will showcase experimental evidence supporting altermagnetism, including its distinct signatures in photoemission spectra [4] and nanoscale mapping [5]. Finally, we will explore emerging research directions such as altermagnetic spintronics [6], magnonics [7], two-dimensional magnetism [8], and multiferroics [9], along with potential applications of altermagnets both within and beyond solid-state physics [10], including their use in ultrafast and low-power nanoelectronics.

References

[1] L. Šmejkal, J. Sinova, and T. Jungwirth, “Beyond Conventional Ferromagnetism and Antiferromagnetism: A Phase with Nonrelativistic Spin and Crystal Rotation Symmetry,” Phys. Rev. X, vol. 12, no. 3, Sept. 2022, https://doi.org/10.1103/physrevx.12.031042
[2] I. I. Mazin, K. Koepernik, M. D. Johannes, R. González-Hernández, and L. Šmejkal, “Prediction of unconventional magnetism in doped FeSb2,” Proc. Natl. Acad. Sci. U.S.A., vol. 118, no. 42, Oct. 2021, https://doi.org/10.1073/pnas.2108924118
[3] A. B. Hellenes, T. Jungwirth, R. Jaeschke-Ubiergo, A. Chakraborty, J. Sinova, and L. Šmejkal, “P-wave magnets,” 2023, arXiv. https://doi.org/10.48550/ARXIV.2309.01607
[4] J. Krempaský et al., “Altermagnetic lifting of Kramers spin degeneracy,” Nature, vol. 626, no. 7999, pp. 517–522, Feb. 2024, https://doi.org/10.1038/s41586-023-06907-7
[5] O. J. Amin et al., “Nanoscale imaging and control of altermagnetism in MnTe,” Nature, vol. 636, no. 8042, pp. 348–353, Dec. 2024, https://doi.org/10.1038/s41586-024-08234-x
[6] L. Šmejkal, A. B. Hellenes, R. González-Hernández, J. Sinova, and T. Jungwirth, “Giant and Tunneling Magnetoresistance in Unconventional Collinear Antiferromagnets with Nonrelativistic Spin-Momentum Coupling,” Phys. Rev. X, vol. 12, no. 1, Feb. 2022, https://doi.org/10.1103/physrevx.12.011028
[7] L. Šmejkal et al., “Chiral Magnons in Altermagnetic RuO2,” Phys. Rev. Lett., vol. 131, no. 25, Dec. 2023, https://doi.org/10.1103/physrevlett.131.256703
[8] I. Mazin, R. González-Hernández, and L. Šmejkal, “Induced Monolayer Altermagnetism in MnP(S,Se)$_3$ and FeSe,” 2023, arXiv. https://doi.org/10.48550/ARXIV.2309.02355
[9] L. Šmejkal, “Altermagnetic multiferroics and altermagnetoelectric effect,” 2024, arXiv. https://doi.org/10.48550/ARXIV.2411.19928
[10] articles from web, https://www.economist.com/science-and-technology/2024/01/24/scientists-have-found-a-new-kind-of-magnetic-material , https://www.science.org/content/article/researchers-discover-new-kind-magnetism

Speaker: Libor Šmejkal

17 Differential Isotropic Model of Ferromagnetic Hysteresis: Temperature Dependence of Saturation Magnetization and Cluster Magnetic Moment

A new differential isotropic model of ferromagnetic hysteresis (DIMFH) [1] has been developed, which has removed the contradictions and ambiguities in the original Jiles-Atherton (J-A) model. This model is simpler, uses only 4 parameters ($M_s$, $a$, $h$, $β$) with clear physical meaning and is based on a new assumption: the existence of so-called magnetic clusters - a coherent regions of ferromagnetic material with size of $10^4$ - $10^6$ of Bohr magnetons. Magnetic clusters form an intermediate stage between atomic magnetic moments and magnetic domains.

In this paper we focus our attention to one of the unsolved problems of the DIMFH: the influence of temperature on the saturation magnetization $M_s$ and on the average magnitude of the cluster magnetic moment $m$. Magnetization curves of an amorphous Fe$_{77.5}$Si$_{7.5}$B$_{15}$ ribbon sample were measured from room temperature up to $400$ °C and successfully fitted by the DIMFH model with high precision. Temperature dependence of $M_s$ parameter is correlated with a simple two-level system model with Weiss approximation. The fitted values of Weiss coefficient $w = 284.56$ and number of Bohr magnetons $N \approx 2$ are in good agreement with literature for systems containing iron [2]. The $w$ coefficient is further compared to the DIMFH parameter $\beta$ describing average mutual interaction between magnetic clusters. Differences in $w$ and $\beta$ values are discussed in detail.

The magnetic moment cluster $m$ is related to the thermodynamic temperature $T$ through the parameter $a$ of the DIMFH model using the relation $a \equiv \frac{k_\mathrm{B}T}{\mu_0 m}$, where $k_\mathrm{B}$ and $\mu_0$ are the Boltzmann constant and vacuum permeability, respectively. By fitting magnetization curves at different temperatures using the DIMFH model, a linear decrease in the parameter $a$ with increasing temperature T was determined. Such conclusion supports an idea that the magnitude of the magnetic cluster $m$ increases during the system heating. For a room temperature, cluster size of $1.25 \cdot 10^5$ Bohr magnetons is calculated, while for $250$ °C, size of $2.86 \cdot 10^5$ Bohr magnetons is obtained. For higher temperatures approaching the Curie temperature, the assumptions of the DIMFH model are not valid.

Acknowledgements

This work was supported by the Ministry of Education, Youth and Sports of the Czech Republic, projects no. CZ.02.1.01/0.0/0.0/17_048/0007399 and SP2025/009.

References

[1] J. Pytlík et al., “Differential isotropic model of ferromagnetic hysteresis,” Physical Review B, vol. 108, no. 10. American Physical Society (APS), Sep. 15, 2023. https://doi.org/10.1103/physrevb.108.104414
[2] D. Jiles, „Introduction to magnetism and magnetic materials. Third edition.” Boca Raton: CRC Press, Taylor & Francis Group, 2016. ISBN 978-1-4822-3887-7

Speaker: Jan Pytlík (Department of Physics, VSB – Technical University of Ostrava, 17. listopadu 2172/15, Ostrava, Czech Republic)

18 Thermal Phase Transitions of Spin-$1/2$ Ising-Heisenberg Model on the Extended Lieb Lattice in a Magnetic Field

The spin-$1/2$ Ising-Heisenberg model on the extended Lieb lattice in a magnetic field is solved using a combination of analytical and numerical methods. The decoration-iteration transformation [1] maps this model onto a spin-$1/2$ Ising model on the square lattice in an effective field, which can be solved exactly provided that the effective field becomes zero. Classical Monte Carlo simulations are then employed for the effective spin-$1/2$ Ising model on the square lattice, from which one may extract according to exact mapping correspondence rigorous numerical results for the spin-$1/2$ Ising-Heisenberg model on the extended Lieb lattice. The exact ground-state phase diagram reveals presence of quantum antiferromagnetic, monomer-dimer, ferrimagnetic, and ferromagnetic phases. In particular, we have explored the magnetization, magnetic susceptibility, entropy, and specific heat at finite temperatures. These quantities are particularly interesting close to a ground-state phase boundary between the monomer-dimer and ferrimagnetic phases, which extends to finite temperatures in the form of a line of discontinuous thermal phase transitions terminating at an Ising critical point. The anomalous response of basic magnetic and thermodynamic quantities can also be found for the quantum aftiferromagnetic phase, which contrarily exhibits at a given magnetic field a line of continuous thermal phase transitions.

Acknowledgements

This work was financially supported by The Ministry of Education, Research, Development and Youth of the Slovak Republic under the grant No. VEGA 1/0298/25, by the Slovak Research and Development Agency under Contract No. APVV-20-0150, and by the internal grant of Faculty of Science of Pavol Jozef Šafárik University in Košice under the contract No. VVGS-2025-3497.

References

[1] J. Strečka, “Generalized algebraic transformations and exactly solvable classical-quantum models,” Physics Letters A, vol. 374, no. 36. Elsevier BV, pp. 3718–3722, Aug. 2010. https://doi.org/10.1016/j.physleta.2010.07.030

Speaker: Jozef Strecka (Pavol Jozef Šafárik University in Košice, Faculty of Science, Institute of Physics)

19 Electric-Field Driven Flat Band in Distorted Sawtooth Chain

We investigate a paradigmatic model of a frustrated spin system - the sawtooth chain with magnetoelectric coupling - realized through the Katsura-Nagaosa-Balatsky (KNB) mechanism. While an applied magnetic field influences the spin system via the conventional Zeeman term, the electric field couples to the spins through the KNB mechanism, effectively manifesting as a Dzyaloshinskii-Moriya interaction. This interaction depends on the magnitude and direction of the electric field, as well as the geometry of the lattice. In our previous work [1], we demonstrated that an appropriately applied electric field can drive the spin system into a flat-band scenario, thereby circumventing the need for fine-tuned exchange couplings. Specifically, when the electric field is aligned along the basal line of the chain, the saturation magnetic field is reduced. Here, we find that the system exhibits a magnetization jump induced by the electric field, as well as a polarization jump driven by the magnetic field, highlighting a strong magnetoelectric response and an enhanced electrocaloric effect. Furthermore, by considering a generalized sawtooth chain with lattice structure asymmetry, we uncover additional ways to induce a flat-band regime in the one-magnon spectrum through special selection of the electric field’s direction and magnitude.

References

[1] J. Richter et al., “Electric field driven flat bands: Enhanced magnetoelectric and electrocaloric effects in frustrated quantum magnets,” Physical Review B, vol. 105, no. 5. American Physical Society (APS), Feb. 18, 2022. https://doi.org/10.1103/physrevb.105.054420

Speaker: Vadim Ohanyan (Yerevan State University & CANDLE Synchrotron Research Institute)

20 The Role of Orbital Angular Momentum in Topologically Non-Trivial Altermagnetic Systems

The emerging field of altermagnetism combines the merits of both ferromagnets and antiferromagnets, which, until recently, were thought to be incompatible. Consequently, altermagnets exhibit phenomena unmatched by either of these two traditional magnetic phases [1]. Despite the tremendous interest in this novel magnetic phase, the possible relation of altermagnetism to topology has been discussed in only a few cases. Before addressing the role of topology, it is first necessary to examine the role of orbital angular momentum (OAM) in topologically trivial systems. Overall, experimental investigations of the OAM character in altermagnets are of fundamental importance, as they provide essential insights into the underlying wavefunction character of altermagnets and, owing to the topological robustness of their subset - Weyl altermagnets - open avenues for applications in electronic and spintronic devices. We will first introduce the role of OAM and Berry curvature in topologically non-trivial systems. Consequently, we will foreshadow how dichroic techniques can be used to address these initial state wavefunction properties. More broadly, we will discuss OAM in both non-centrosymmetric [2-4] and inversion-symmetric [5] systems with a focus on the implications of OAM occurrence in altermagnetic systems.

Acknowledgements

J.S. would like to thank the QM4ST project with Reg. No. CZ.02.01.01/00/22 008/0004572,cofounded by the ERDF as part of the MŠMT.

References

[1] J. Krempaský et al., “Altermagnetic lifting of Kramers spin degeneracy,” Nature, vol. 626, no. 7999. Springer Science and Business Media LLC, pp. 517–522, Feb. 14, 2024. https://doi.org/10.1038/s41586-023-06907-7
[2] J. Schusser et al., “Assessing Nontrivial Topology in Weyl Semimetals by Dichroic Photoemission,” Physical Review Letters, vol. 129, no. 24. American Physical Society (APS), Dec. 09, 2022. https://doi.org/10.1103/physrevlett.129.246404
[3] J. Schusser et al., “Towards robust dichroism in angle-resolved photoemission,” Communications Physics, vol. 7, no. 1. Springer Science and Business Media LLC, Aug. 08, 2024. https://doi.org/10.1038/s42005-024-01762-y
[4] T. Figgemeier et al., “Imaging Orbital Vortex Lines in Three-Dimensional Momentum Space,” Physical Review X, vol. 15, no. 1. American Physical Society (APS), Feb. 13, 2025. https://doi.org/10.1103/physrevx.15.011032
[5] I. Sidilkover et al., „Reexamining circular dichroism in photoemission from a topological insulator“, in preparation.

Speaker: Jakub Schusser (University of West Bohemia)

21 Generalized $2$D Planar Rotator Models With Arbitrary Number of Phase Transitions and Various Universality Classes

The Mermin-Wagner theorem states that in a two-dimensional $XY$ (or planar rotator) model with nearest-neighbor interactions the continuous symmetry cannot be broken and thus no standard phase transition can occur. Nevertheless, the model is well known to show a so-called Berezinskii-Kosterlitz-Thouless (BKT) phase transition due to the presence of topological excitations, called vortices and antivortices. At the BKT transition the vortices and antivortices bind in pairs, which results in an algebraic decay of the correlation function within the quasi-long-range-ordered BKT phase below the BKT transition temperature $T_{\rm BKT}$.

The standard planar rotator model can be generalized by including (pseudo)nematic higher-order coupling terms, which give rise to further, fractional vortex excitations. The presence of both integer and fractional vortices can lead to a richer critical behavior and such models have been demonstrated to show up to three different phase transitions as a function of temperature [1]. Here, we propose related models that can display even an arbitrary number of phase transitions belonging to different universality classes. The models are based on the standard two-dimensional planar rotator model, which is generalized by including $n$ higher-order nematic terms with exponentially increasing order $q^k$, $k = 1,\dots,n$, and linearly increasing interaction strength.

By employing Monte Carlo simulation, we demonstrate that under certain conditions the number of phase transitions in such models is equal to the number of terms in the generalized Hamiltonian and thus it can be predetermined by construction [2]. The proposed models produce the desirable number of phase transitions by solely varying the temperature. With decreasing temperature, the system passes through a sequence of different phases with gradually decreasing symmetries. A finite-size scaling analysis shows that the corresponding phase transitions all start at higher temperatures with the (no spontaneous symmetry breaking) BKT transition and may proceed through a sequence of discrete $\mathbb{Z}_q$ symmetry-breaking transitions between different nematic phases down to the lowest-temperature ferromagnetic phase. More specifically, for the higher-order nematic terms that exponentially increase with the basis $q = 2$ and $4$ the remaining transitions below $T_{\rm BKT}$ are found to belong to the Ising, for $q = 3$ to the three-state Potts, and for $q \geq 5$ to the BKT universality classes.

Acknowledgements

This research was funded by the projects VEGA 1/0695/23 and APVV-20-0150.

References

[1] F.C. Poderoso et al., “New Ordered Phases in a Class of Generalized XY Models” Physical Review Letters, vol. 106, no. 6. American Physical Society (APS), Feb. 10, 2011. https://doi.org/10.1103/physrevlett.106.067202
[2] M. Žukovič, “Generalized XY Models with Arbitrary Number of Phase Transitions,” Entropy, vol. 26, no. 11. MDPI AG, p. 893, Oct. 23, 2024. https://doi.org/10.3390/e26110893

Speaker: Prof. Milan Žukovič (Pavol Jozef Šafárik University in Košice, Institute of Physics)

12:45 PM LUNCH

Section S6: Low-dimensional magnetic materials, molecular magnets and ferrofluids - PART 1

Convener: Sergei Zvyagin (Dresden High Magnetic Field Laboratory (HLD-HZDR))

22 A Frustrated Antipolar Analogue to the Classical Spin Liquid in Triangular Lattice EuAl$_{12}$O$_{19}$

The ground-state of the $S =1/2$ Ising 2D Triangular Lattice AntiFerroMagnet (ITLAFM) is the go-to example of a frustrated magnet, and was calculated by Wannier over $70$ years ago [1]. In the absence of strong quantum fluctuations, this ground-state is called a classical spin liquid with a large number of energy-degenerate spin configurations that share the minimum energy. It is expected to have spin-dynamics governed by Arrhenius behavior, with spinons required to transform between each topologically protected configuration [2]. Despite interest in investigating this type of system experimentally, model magnetic materials are hard to come by, with magnetic moments typically deviating from the Ising limit or displaying significant quantum fluctuations.

The rare-earth hexaaluminates with the magnetoplumbite structure are a promising family for the investigation of ITLAFM physics, and I will present our investigations of the compound EuAl$_{12}$O$_{19}$. Despite the well separated triangular layers of magnetic ions, the Eu$^{2+}$ magnetic interactions drive the material to ferromagnetism with a $T_C = 1.3$ K [3].

Instead, we find the sought-after classic-liquid physics of the ITLAFM ground-state not within its magnetic lattice, but within a lattice of antiferroelectrically coupled dipoles. The material contains a triangular lattice of dynamically disordered, but antiferroelectrically correlated, charge displacive dipoles built from Al$^{3+}$ ions sitting off-centre within their bipyramid oxygen cages. Electric dipoles have an advantage over spins that they can be intrinsically Ising, and we label this model instead the Ising Triangular Lattice AntiFerroElectric (ILAFE). I will present our recently published structural, spectroscopic, and thermodynamic measurements on EuAl$_{12}$O$_{19}$, comparing the observed properties to those expected for the ITLAFM [4].

References

[1] G. H. Wannier, “Antiferromagnetism. The Triangular Ising Net,” Physical Review, vol. 79, no. 2. American Physical Society (APS), pp. 357–364, Jul. 15, 1950. https://doi.org/10.1103/physrev.79.357
[2] Z. Zhou et al., “Quantum dynamics of topological strings in a frustrated Ising antiferromagnet,” npj Quantum Materials, vol. 7, no. 1. Springer Science and Business Media LLC, Jun. 08, 2022. https://doi.org/10.1038/s41535-022-00465-3
[3] G. Bastien et al.,"Quasi-two-dimensional ferromagnetism in the triangular magnet EuAl12⁢O19" Physical Review B, vol. 110, no. 9. American Physical Society (APS), Sep. 24, 2024. https://doi.org/10.1103/physrevb.110.094436
[4] G. Bastien et al., “A Frustrated Antipolar Phase Analogous to Classical Spin Liquids,” Advanced Materials, vol. 36, no. 50. Wiley, Oct. 23, 2024. https://doi.org/10.1002/adma.202410282

Speaker: Ross Colman (Department of Condensed Matter Physics, Charles University, Prague, Czech Republic)

23 Magnetism and Excitations in Quasi-$2$D Materials Under External Perturbations: Microscopic Understanding

Magnetic van der Waals materials with very weak exchange interaction between magnetically ordered layers represent an interesting intermediate stage between the more explored cases of isotropic bulk-like exchange and the recently intensively studied ideal $2$D limit (monolayer) [1]. We perform a complex investigation of lattice and magnetic excitations induced by external perturbations employing the DFT calculations, and compare it to infrared, terahertz, and Raman spectroscopy results in such material, trihalide VI$_3$. We find that the transition to the long-range ferromagnetic order is accompanied by the observed variations of phonon frequencies induced by the strong magnetoelastic coupling. The acoustic magnon mode acquires here unusually high energy reaching to THz range, but dramatically softens at temperatures where a second lattice distortion has been reported in the literature [2]. First-principles calculations show the strong connection of magnetic ordering to the lattice. Furthermore, a ground state with an exceptionally high orbital momentum is predicted, and the electronic configuration is compared to recent measurements based on the x-ray magnetic circular dichroism [3]. These findings suggest the possibility of controlling magnetic anisotropy in this system by selective occupation of specific lattice modes.

A highly interesting connection between the formation of helimagnetic order and breaking of both inversion and rotational symmetry of the lattice has been recently discovered in single-layer Ni dihalides [4]. Here we examine how magnetic order in NiBr$_2$ is affected by pressure. We show that the interlayer exchange interaction plays here a key role in the selection of the most favorable magnetic order.

References

[1] M. Gibertini et al., “Magnetic 2D materials and heterostructures,” Nature Nanotechnology, vol. 14, no. 5. Springer Science and Business Media LLC, pp. 408–419, May 2019. https://doi.org/10.1038/s41565-019-0438-6
[2] D. Hovančík et al., “Terahertz Magnetic and Lattice Excitations in van der Waals Ferromagnet VI3,” The Journal of Physical Chemistry Letters, vol. 13, no. 48. American Chemical Society (ACS), pp. 11095–11104, Nov. 23, 2022. https://doi.org/10.1021/acs.jpclett.2c02944
[3] D. Hovančík et al., “Large Orbital Magnetic Moment in VI3,” Nano Letters, vol. 23, no. 4. American Chemical Society (ACS), pp. 1175–1180, Feb. 01, 2023. https://doi.org/10.1021/acs.nanolett.2c04045
[4] Q. Song et al., “Evidence for a single-layer van der Waals multiferroic,” Nature, vol. 602, no. 7898. Springer Science and Business Media LLC, pp. 601–605, Feb. 23, 2022. https://doi.org/10.1038/s41586-021-04337-x.

Speaker: Karel Carva (Charles University)

24 Magneto-Elastic Interaction in Y$_3$Cu$_9$(OH)$_{19}$Cl$_{8}$

Quantum Spin Liquid (QSL) is a ground state of condensed matter, which is characterized by the absence of magnetic order down to the lowest temperatures along with long-range entanglement of fluctuating spin excitations [1]. Such a state of matter can be promoted by magnetic frustration which prevents the magnetic moments from antiferromagnetic ordering. There are many lattices created by magnetic ions exhibiting magnetic frustration. One of them is the two-dimensional kagome lattice with a high degree of frustration consisting of corner-sharing equilateral triangles. Although the concept is simple, finding such compounds with paramagnetic ions on a regular kagome lattice is quite complicated. The mineral herbertsmithite was considered as a very promising compound, but here the kagome lattice contains impurity spins created by the partial mixing of Zn and Cu atoms within and between the kagome planes. As a consequence, the magnetic properties at low temperatures are dominated by these impurities. Here we present the study of a related compound to herbertsmithite having a slightly distorted kagome lattice, but without impurity spins.

Y-kapellasite is yttrium copper hydroxychloride with the chemical formula Y$_3$Cu$_9$(OH)$_{19}$Cl$_8$, crystallizing in the rhombohedral crystal structure $R-3$ (148) [2]. The compound is antiferromagnetic below $T_N = 2.2$ K [2]. An anomalous behavior was found in the temperature dependence of thermal expansion around $32$ K, measured by dilatometry [3]. This finding rises the question whether there is any structural transition, but the X-ray and neutron diffraction experiments were inconclusive. We present the study of lattice dynamics studied by infrared spectroscopy. The obtained results are compared with the ab initio calculations and suggest the lowering of crystal lattice symmetry. The main crystal modification is probably caused by H atoms. We also observed the softening of low-energy phonons, which can be a sign of enhanced magnetoelastic interactions.

Acknowledgements

This work was supported by the Czech Science Foundation - project GAČR 23-06810O.

References

[1] L. Balents, “Spin liquids in frustrated magnets,” Nature, vol. 464, no. 7286. Springer Science and Business Media LLC, pp. 199–208, Mar. 10, 2010. https://doi.org/10.1038/nature08917
[2] P. Puphal et al., “Kagome quantum spin systems in the atacamite family,” Physical Review Materials, vol. 2, no. 6. American Physical Society (APS), Jun. 29, 2018. https://doi.org/10.1103/physrevmaterials.2.063402
[3] D. Chatterjee et al., "From spin liquid to magnetic ordering in the anisotropic kagome Y-kapellasite Y3Cu9(OH)19Cl8: A single-crystal study," Physical Review B, vol. 107, no. 12. American Physical Society (APS), Mar. 28, 2023. https://doi.org/10.1103/physrevb.107.125156

Speaker: Petr Doležal (Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University)

25 Energy Harvesting by Ferrofluids

The increasing demand for energy harvesting is associated with the current era of big data, when a problem of power supply of numerous distributed sensors must be addressed. A recent research attention has been paid to ferrofluids in the role of a nanogenerator’s active medium. Efforts have been put in development of ferrofluid-based triboelectric nanogenerators and piezoelectric energy harvesters. However, ferrofluids have gained recognition primarily for their great potential in electromagnetic energy harvesting systems, utilizing the basic principles of electromagnetic induction. In contrast to conventional electromagnetic generators that rely on solid moving magnets, ferrofluids enable creation of generators of light-weight, smaller size and flexible shapes.

In our study, we have prepared five ferrofluid samples based on biodegradable transformer oil. The ferrofluids with different iron oxide nanoparticle concentrations were subjected to investigation of vibrational energy harvesting utilizing the ferrofluid sloshing (volume of 2.5 ml). This enables us to obtain the dependence of the electromotive force on the ferrofluid magnetization of saturation. We also study the electromagnetic induction by ferrofluid sloshing in various magnetic field configurations. The ferrofluid sloshing is excited by a laboratory shaker and the induced voltage is studied under both, increasing and decreasing shaking rates (frequency). It is found that the most effective energy harvesting is achieved in the magnetic field of 15 mT generated by a single permanent magnet attached to the ferrofluid vial side wall, providing the field intensity perpendicular to the axis of the vial motion and gravity. The maximal mean power achieved with the ferrofluid is 233 nW. In conversion, it is 93 nW per milliliter of the ferrofluid. The increasing magnetization of saturation yields the increase in the harvested power except of the ferrofluid sloshing in the magnetic field of the single magnet attached to the bottom of the horizontal vial, when the opposite effect is observed. The dependence of the mean induced voltage on the vial oscillation frequency is identical for measurements in acceleration and deceleration mode and this behavior holds for each magnetic field configuration and each ferrofluid concentration.

Acknowledgements

This work is funded by Slovak Academy of Sciences and Ministry of Education in the framework of projects VEGA 2/0029/24, and Slovak Research and Development Agency under the contract No. APVV-22-0115.

Speaker: Dr Michal Rajňák (Institute of Experimental Physics, Slovak Academy of Sciences)

26 Influence of Magnetic Field Averaging on Modeling Magnetic Properties of Molecular Nanomagnets

Accurate modelling of the magnetic properties of powder samples, particularly molecular nanomagnets, requires careful consideration of magnetic field averaging due to the random orientation of the applied field relative to individual crystallites. In this study, we employ the exact diagonalization method to compute key magnetic properties, such as magnetization and magnetic susceptibility, under different field averaging schemes. We investigate the validity of commonly used approximations and compare them with more sophisticated averaging methods. Our results demonstrate that for spin $s=1$, the conventional averaging approach—where only the $z$ and $x$ directions of the applied magnetic field are considered, with weights of $1/3$ and $2/3$, respectively—yields results nearly identical to those obtained through more detailed averaging techniques. However, for larger spin values, the choice of averaging method becomes increasingly critical, as improper field averaging can lead to significant deviations in calculated magnetic properties.

Additionally, we explore the role of magnetic anisotropy in influencing the powder-averaged magnetization and susceptibility, highlighting cases where strong anisotropy leads to noticeable deviations from isotropic expectations. To improve the accuracy of our modelling, we analyse the proper distribution of points on a sphere for orientational averaging, following established mathematical approaches while considering the symmetry between the $x$ and $y$ directions. Unlike Monte Carlo-based methods, which rely on stochastic sampling, our approach ensures systematic and reproducible results by employing well-defined sphere point distributions.

Our findings emphasize the necessity of selecting an appropriate averaging scheme when modelling powder samples, particularly for systems with high spin or pronounced anisotropy. The insights gained from this study contribute to the refinement of theoretical models and provide guidance for interpreting experimental data on molecular nanomagnets.

Speaker: Dr Michał Antkowiak (Adam Mickiewicz University)

27 Exploration of Large Coordination Clusters and Their Switchability

Multifunctional molecular materials based on coordination polynuclear multi-site molecules lie at the heart of materials science in view of growing technological challenges dedicated to the progressive miniaturization process and required high operation speed in information processing, quantum computing, and spintronics. Invariably particular interest in research is focused on molecular materials combining several desirable physicochemical properties to conform switchability regime, and thus, to constituting the physical basis for recording, reading, and processing information. We have focused in our work on modular approach, which originally is based on combination of different metal ions or larger molecular fragments in molecular architecture. This is an acknowledged way to gain a variety of unique structural motives and material properties involving e.g. electronic conduction, charge transfer, spin crossover, noncentrosymmetry, luminescence, second-harmonic generation [1]. In this context, one of the perfect candidates for our consideration are molecular compounds with two or more inequivalent spin states, which could be switched by convenient external stimulus such as temperature, light, electric current, sorption/desorption or chemical activation.

The presentation will focus on the design strategies, synthesis and physicochemical properties of two families of large molecular clusters with switchable magnetic properties. In particular architectures of {M$_9$[M$^{\prime}$(CN)$_8$]$_6$(MeOH)$_{24}$}$\cdot$solv (M = Co$^{2+}$, Ni$^{2+}$, Fe$^{2+}$, Mn$^{2+}$, M$^{\prime}$ = W$^{\rm V}$, Re$^{\rm V}$) and {Fe[Fe(bzbpen)]$_6$[W$^{\rm V}$(CN)$_8$]$_2$[W$^{\rm IV}$(CN)$_8$]$_2$}$\cdot$solv clusters representing switchable magnetic properties realized via spin crossover (SCO) or electron transfer (ET) phenomena stimulated by temperature or sorption/desorption of solvents [2,3]. Moreover, the presentation will explore further concepts of reversible spin state switching implementation via light-driven cyclization or isomerization of photochromic organic ligands from the diarylethenes and azobenzenes group.

Acknowledgements

We gratefully acknowledge National Science Centre (Poland) project number 2019/35/B/ST5/01481

References

[1] J. Kobylarczyk et al., “Modular approach towards functional multimetallic coordination clusters,” Coordination Chemistry Reviews, vol. 419. Elsevier BV, p. 213394, Sep. 2020. https://doi.org/10.1016/j.ccr.2020.213394
[2] L. Shi et al., “Site Selectivity for the Spin States and Spin Crossover in Undecanuclear Heterometallic Cyanido-Bridged Clusters,” Inorganic Chemistry, vol. 62, no. 18. American Chemical Society (ACS), pp. 7032–7044, Apr. 25, 2023. https://doi.org/10.1021/acs.inorgchem.3c00325
[3] J. Kobylarczyk et al., “Tuning of the phase transition between site selective SCO and intermetallic ET in trimetallic magnetic cyanido-bridged clusters,” Dalton Transactions, vol. 49, no. 47. Royal Society of Chemistry (RSC), pp. 17321–17330, 2020. https://doi.org/10.1039/d0dt03340e

Speaker: Jedrzej Kobylarczyk (Institute of Nuclear Physics, Polish Academy of Sciences)

28 EPR Study of Spin Anisotropies in the $S=1/2$ Spatially Anisotropic Triangular Quantum Magnet Cu($tn$)Cl$_2$

Cu($tn$)Cl$_2$ ($tn$ = C$_3$H$_{10}$N$_2$) represents a quasi-two-dimensional ($2$D) quantum magnet which preserves $2$D features far below the phase transition to the ordered state at $0.55$ K. The coexistence of $2$D and long-range magnetic correlations can be ascribed to the incommensurate modulated crystal structure. The modulation leads to the formation of extremely thin regions with a thickness running from one to four unit cells which differ in the orientation of $tn$ ligands. Since previous ab initio studies revealed high sensitivity of exchange interactions on the $tn$ positions, large variability of exchange couplings in such confined $2$D geometries can preserve the $2$D correlations. The inclusion of the two strongest nearest-neighbor exchange couplings from those provided by the ab initio studies leads to formation of effective rectangular lattice. While excellent agreement between specific heat data and the theory was achieved, significant deviations appear in the description of magnetic susceptibility and magnetic phase diagram, where additional phase in the vicinity of a critical region was observed [1]. Since the phase appears in the fields perpendicular to the direction of the modulation vector, its dependence on the field orientation may be caused by the spatial and spin anisotropies. The latter can be estimated from the electron paramagnetic resonance (EPR) spectra.

Present work is devoted to the X-band single crystal studies of angular and temperature dependence of EPR spectra providing information about the $g$-factors and linewidth $\Delta B$. The analysis of temperature dependence of linewidth along the $a$ and $b$ axis enabled the estimation of spin anisotropies. In the field parallel to $a$ axis which is perpendicular to modulation vector, the linewidth is determined by the contribution of antisymmetric Dzyaloshinskii-Moriya (DM) interaction, symmetric spin anisotropies of dipolar origin $K^{dip}$ and exchange anisotropy $K^{ea}$. The absence of additional phase in the magnetic phase diagram along the $b$ axis suggests that the DM contribution along the $b$ axis could be neglected and a major part of linewidth can be ascribed mainly to $K^{dip}$ and $K^{ea}$ anisotropies, which are always present in real materials. On the other hand, occurrence of DM interaction depends on the crystal symmetry. The possibility of EPR studies at higher frequencies is discussed for other characterization of spin anisotropies in Cu($tn$)Cl$_2$.

Acknowledgements

The financial support of projects VEGA 1/0132/22, APVV-18-0197 and APVV-22-0172 is acknowledged.

References

[1] R. Tarasenko et al., “Extraordinary two-dimensionality in the S = 1/2 spatially anisotropic triangular quantum magnet Cu(1,3-diaminopropane)Cl2 with modulated structure,” Physical Review B, vol. 108, no. 21. American Physical Society (APS), Dec. 28, 2023. https://doi.org/10.1103/physrevb.108.214432

Speaker: Ali Darwich (Pavol Jozef Safarik University)

4:00 PM Coffee break

Section S2: Amorphous, nanocrystalline and other soft magnetic materials - PART 1

Convener: Prof. Peter Kollár (Pavol Jozef Šafárik University in Košice, Faculty of Science, Institute of Physics)

29 Soft Magnetic Nanocrystalline Alloys Prepared by Ultra-Rapid Annealing

Nanocrystalline alloys represent an important class of soft magnetic materials. Their technological relevance stems from a combination of high saturation flux density, excellent permeability, and low core loss. Further improvements in magnetic performance can be achieved through careful compositional tuning and advanced processing techniques that optimize phase content and reduce grain size.

This work focuses on the ultra-rapid annealing technique, which involves compressing samples between pre-heated Cu blocks. The exceptionally high heating rates and short processing times promote the formation of finer nanocrystalline grains compared to conventional furnace annealing [1]. Two recent case studies on ultra-rapid annealing will be presented.

The first study examines the impact of elevated temperatures on the soft magnetic properties of ultra-rapidly annealed high-Bs Fe-Co-B-(Cu) and Fe-Co-Si-B-(P) nanocrystalline alloys with reduced metalloid content. Hysteresis loops were measured from room temperature (RT) to $300$°C using a Förster-type B-H loop tracer with a built-in furnace inside a magnetically shielded room. Understanding the thermal stability of ultra-rapidly annealed nanocrystalline alloys is essential for assessing their application potential, particularly for components exposed to high-temperature environments. Our experiments demonstrate that high-Bs Fe-Co-B-(Cu) alloys exhibit very good thermal stability, maintaining excellent soft magnetic characteristics between $30–250$°C, making them promising candidates for elevated-temperature applications.

The second study investigates the effects of conventional and ultra-rapid thermal processing on the amorphous-to-crystalline transformation and soft magnetic properties of Ni-rich Fe-Ni-Nb-B rapidly quenched ribbons. A sample with the composition (Fe$_{0.25}$Ni$_{0.75}$)$_{81}$Nb$_7$B$_{12}$ exhibits a significant degradation in soft magnetic properties after conventional annealing for $60$ min at $435$°C, with coercivity increasing to $550$ A/m due to the formation of large fcc-type (Fe-Ni)$_{23}$B$_6$ grains coexisting with fcc-FeNi nanograins. In contrast, ultra-rapid annealing for one second at $520$°C effectively suppresses the formation of unwanted (Fe-Ni)$_{23}$B$_6$ grains, resulting only in ultrafine fcc-FeNi grains ($5–8$ nm). This process reduces the coercivity to just $2.3$ A/m achieving a superior $H_c$ value for FeNi-based nanocrystalline alloys with permalloy-like ferromagnetic grains.

Acknowledgements

This research was supported by the projects APVV 23-0281, VEGA 2/0148/23 and JRP SAS-TUBITAK NOMAGRAD.

References

[1] B. Kunca et al., “Soft magnetic performance of ultra-rapidly annealed high-Bs Fe-(Co)-B nanocrystalline alloys at elevated temperatures,” Journal of Alloys and Compounds, vol. 911. Elsevier BV, p. 165033, Aug. 2022. https://doi.org/10.1016/j.jallcom.2022.165033

Speaker: Dr Ivan Škorvánek (Institute of Experimental Physics, Slovak Academy of Sciences)

30 Magnetic Behavior of Nanostructured and Far-From-Equilibrium Complex Oxides

The straightforward synthesis of inorganic materials, especially in the nanostructured and far-from-equilibrium states, is a great challenge despite promising developments of preparation techniques [1]. The present work provides a brief overview of the mechanochemically synthesized complex oxides. The “green” aspects of mechanochemistry are clearly illustrated by selected examples, where highly defective and metastable nanostructured complex oxides with distinctive functionalities are mechanochemically synthesized in a single processing step at ambient temperature, without the need for solvents and/or calcination under controlled oxygen fugacity. Comprehensive spectroscopic techniques provide detailed complementary atomic-scale insights into the nature of the local short-range disorder of nanostructured oxides. The selected examples of both enhanced and deteriorated magnetic properties of nanoceramics prepared via mechanochemistry are presented with the focus on the clear-cut explanation of the interplay between their short-range structural disorder and magnetism. The responses of the far-from-equilibrium nanooxides to the external stimuli will also be highlighted.

Acknowledgements

The support by the Deutsche Forschungsgemeinschaft (DFG) within the project SE 1407/4 is acknowledged.

References

[1] V. Šepelák et al., “One-Step Mechanochemical Synthesis of Nanostructured and Non-Equilibrium Complex Oxides,” Encyclopedia of Green Chemistry. Elsevier, pp. 473–482, 2025. https://doi.org/10.1016/b978-0-443-15742-4.00006-5

Speaker: Vladimír Šepelák (Karlsruhe Institute of Technology)

31 Modeling the Effect of Stress on the Magnetization Curves as a Simple Magnetic Field Scaling

The mechanical stress strongly influences the magnetic properties of ferromagnetic materials - the magnetic hysteresis loops measured under constant stress.

In 1930 Kersten analyzed the total energy of a stressed ferromagnet and derived the analytical expression for the relative initial susceptibility that is inversely proportional to the stress for the initial part of the magnetization curve [1]:
$$ \chi = M/H = JS^2/(3\mu_0\gamma_S\sigma).(1)$$ There are many hundreds works on the modeling the effect of stress on the magnetic susceptibility and hysteresis loops [2]. The most popular is the Jiles-Atherton-Sablik model, which is based on the the Jiles-Atherton model with the effective field by stress, which is the function of the stress and the magnetization [3]. Recently we have found that the Kersten relation for a relative susceptibility is also valid for the differential susceptibility of nonlinear $M(H)$ curves of stressed polycrystalline iron-based ferromagnets for any magnetization (not the field) value [4]. The effect of stress is introduced by scaling the magnetic field of the $M(H)$ curve proportionally to stress. This simple relation together with the $M(H)$ curve in the form of the arctangent function gives a very good agreement with experimental curves, reproducing all stress-induced features usually observed on the magnetization curves including the common crossover point. Also it validates the effective field by stress concept used in the Jiles-Atherton-Sablik and its variations. We propose to plot the field and differential susceptibility as a function of magnetization, $H(M)$ and $\chi(M)$ in contrast to convenient $M(H)$ and $\chi(M)$ curves. Then, $\chi(M)$ peaks have the same positions and widths with only difference in the vertical scaling.

Acknowledgements

This work was supported by the Ferroic Multifunctionalities project, supported by the Ministry of Education, Youth, and Sports of the Czech Republic. Project No. CZ.02.01.01/00/22_008/0004591.

References

[1] R.M. Bozorth, Ferromagnetism. Van Nostrand, New York (1951).
[2] A. Kumar and A. Arockiarajan, “Evolution of nonlinear magneto-elastic constitutive laws in ferromagnetic materials: A comprehensive review,” Journal of Magnetism and Magnetic Materials, vol. 546. Elsevier BV, p. 168821, Mar. 2022. https://doi.org/10.1016/j.jmmm.2021.168821
[3] M. J. Sablik and D. C. Jiles, “A model for hysteresis in magnetostriction,” Journal of Applied Physics, vol. 64, no. 10. AIP Publishing, pp. 5402–5404, Nov. 15, 1988. https://doi.org/10.1063/1.342383
[4] A. Perevertov, “A phenomenological magnetomechanical model for hysteresis loops,” 2024, arXiv. https://doi.org/10.48550/ARXIV.2412.08323

Speaker: Alexej Perevertov (FZU - Institute of Physics of the Czech Academy of Sciences, Department of Magnetic Measurements and Materials)

POSTER Session: PART 1 (Topics 2, 3, 5 and 9 )

Conveners: Prof. Pavol Sovák (Pavol Jozef Šafárik University in Košice, Faculty of Science, Institute of Physics), Dr Adriana Zeleňáková (Pavol Jozef Šafárik University in Košice, Faculty of Science, Institute of Physics)

32 $3$D Hollow Nanostructures: A New Playground for Curvilinear Magnetism

Magnetic nanoparticles have been extensively studied over the past few decades due to their unique magnetic properties, which are strongly influenced by finite size effects and, more prominently, by surface effects resulting from their high surface-to-volume ratio ($R = S/V$). The synthesis of spherical hollow magnetic nanoparticles takes this a step further, significantly enhancing the surface-to-volume ratio [1]. The possibility to synthesize spherical hollow magnetic nanoparticles allows $R$ to be further enhanced with a consequent increase of topological disorder and magnetic frustration, thus opening new perspectives to explore the surface magnetism at the nanoscale. In addition, hollow spherical nanoparticles can be considered as a thin spherical shell, i.e., as one of the simplest $3$D object for studying the effect of curvature at the nanoscale level After a short review about the more exciting results about possibility to prepare different hollow nanostructures, this talk will present a comparative study of the morpho-structural and magnetic properties of full and hollow maghemite ($\gamma$-Fe$_2$O$_3$) nanoparticles, characterized by large surface to volume ratio, of corresponding sizes $\sim 5.0$nm and $\sim 7.5$nm. These systems have been thoroughly characterized by means of DC and AC magnetization measurement and in field $^{57}$Fe Mössbauer spectrometry. The in-field hyperfine structure analysis confirm the presence of a non-collinear magnetic structure in the hollow NPs, originated from the increased surface effects attributed to their hollow morphology. Interestingly, after field cooling, a horizontal shift of the hysteresis loop was observed, revealing the presence of an exchange bias (EB) effect. The observed EB effect was systematically analyzed in relation to temperature and cooling field parameters. Complementing these experimental results, Monte Carlo (MC) simulations of assemblies of ferrimagnetic hollow nanoparticles revealed that strong exchange coupling between spins in the external thicker surface and at the interface enhances the antiferromagnetic behavior of the hollow nanoparticle, resulting in a decrease of their saturation magnetization (Ms).

Acknowledgements

This work was partially supported by Project funded under the National Recovery and Resilience Plan (NRRP), Mission 4 Component 2 Investment 1.3 - Call for tender No. 1561 of 11.10.2022 of Ministero dell’Università e della Ricerca (MUR); funded by the European Union – NextGenerationEU • Award Number: Project code PE0000021, Concession Decree No. 1561 of 11.10.2022 adopted by Ministero dell’Università e della Ricerca (MUR), CUP D33C22001330002 -Project title “Network 4 Energy Sustainable Transition – NEST

References

[1] F. Sayed et al., “Surface Effects in Ultrathin Iron Oxide Hollow Nanoparticles: Exploring Magnetic Disorder at the Nanoscale,” The Journal of Physical Chemistry C, vol. 122, no. 13. American Chemical Society (ACS), pp. 7516–7524, Mar. 26, 2018. https://doi.org/10.1021/acs.jpcc.8b00300

Speaker: Davide Peddis (Department of Chemistry and Industrial Chemistry & INSTM RU, nM2-Lab, University of Genoa)

33 Analysis of the Components of Energy Losses Fe-based Compacted Powder Material

The soft magnetic compacted powdered materials are used in a variety of electromagnetic applications such as electromotors, magnetic circuits of valves, cores for various inductors in computers, relays, disk drives, printers, hearing aid devices and others. These materials are used due to their relatively easy magnetization and demagnetization, maximum permeability, high magnetic saturation induction, low coercivity, low core losses. Soft magnetic compacted powder materials have high application potential based also on isotropic 3D behaviour, mechanical stability, low-cost production and they offer possibility for environmentally friendly recycling.

This work focuses on the detailed description of the energy loss separation for dc and ac low frequency magnetic fields of Fe-based compacted powder. We analyzed magnetic losses of the soft magnetic materials consisting of iron particles with a size from 125 $\mu$m to 200 $\mu$m according to Bertotti’s and Landgraf’s theories. The surfaces of the iron particles were mechanically smoothed. The ring-shaped compacts were prepared by the high-pressure compaction. The analyze of total energy losses revealed the best magnetic properties of the material with mechanically smoothed surgaces of powder particles.

Particular attention was paid to the processes of mechanical surface treatment of powder particles, coating and pressing, which have a major influence on the final properties of the materials. It is expected that optimization of these processes can significantly reduce energy losses, increase magnetic efficiency and improve the mechanical stability of the materials.

Acknowledgements

This work was funded by Scientific Grant Agency of Ministry of Education of Slovak Republic and Slovak Academy of Science grant numbers VEGA 1/0403/23 and VEGA 1/0016/24.

Speaker: Lívia Provázková (Institute of Manufacturing Management, Faculty of Manufacturing Technologies, Technical University of Košice)

34 Asymmetrical GMI Effect in Cobalt Base Microwires

The asymmetrical GMI ratio dependences of the Co-based microwires recorded during slow magnetization reversal in the longitudinal magnetic field are analyzed in frame of the model of the core-shell domain structure. Considering that Co-based microwire with negative magnetostriction has circularly oriented spontaneous magnetization in the shell, but its narrow core is longitudinally magnetized, there is a transition region in which the vector of spontaneous magnetization must turn by an angle of 90°. During magnetization reversal of the core, the irreversible movement of the single domain wall (Barkhausen jump) is detected [1], which is also manifested by a jump in the asymmetrical double-peak GMI ratio dependences with the maximum value ($\Delta Z/Z$)$_{max}=260\%$ at $H=\pm 2.5$ A/m. Measurements in a Helmholtz coil, which created an additional dc magnetic field, revealed the asymmetrical two-peak behavior of the GMI ratio, corresponding to the rotation of magnetization in the shell after the displacement of domain walls in the core of the Co-based microwire. The achieved high sensitivity of GMI measurements to external dc magnetic field makes the investigated microwires very promising candidates for sensor applications.

Acknowledgements

This research was supported by the Slovak Research and Development Agency under contract No. APVV-16-0079, by VEGA grant No. 1/0350/24 from the Scientific Grant Agency of the Ministry for Education of the Slovak Republic, by the project “Support for the Research and Development Potential in the area of Transportation Vehicles” ITMS 2014+Code 313011T557 and by Foundation Volkswagen Slovakia Grant No. 085/15_RT.

References

[1] J. Kravčák and P. Vrábel, “Onset of Magnetization Reversal in Glass-covered Co-Si-B Microwires,” IEEE Transactions on Magnetics. Institute of Electrical and Electronics Engineers (IEEE), pp. 1–1, 2024. https://doi.org/10.1109/tmag.2024.3446451

Speaker: Dr Jozef Kravčák (Department of Physics, Faculty of Electrical Engineering and Informatics, Technical University of Košice)

35 Comparative Characterization of Structural, Magnetic Properties, and Heating Efficiency of Single- and Multicore Iron Oxide Nanoparticles

Nanotechnology in biomedical applications has enabled the creation of novel systems with unique characteristics that combine the properties of biomolecules and iron oxide nanoparticles (IONPs) [1], enhancing treatment effectiveness and reducing costs. IONPs, valued for their specific magnetic properties and low toxicity, offer a promising approach to overcoming challenges in magnetic hyperthermia. However, their practical application is hindered by low heating power (per unit mass of nanoparticles), which contradicts the expected superparamagnetic behavior of IONPs. This discrepancy is attributed to polydispersity in IONP sizes within real samples or altered magnetic properties due to finite size effects. The solution to this problem is multicore magnetic IONPs resembling flower-like structures. In these nanoflowers (NFs), IONP cores are embedded within a polymer or organic coating, and their unique structure significantly enhances magnetic properties, including strong magnetic responses arising from complex internal magnetic ordering [2].

In this study, single-core and multicore IONPs were synthesized using two methods: coprecipitation and the polyol method. A comprehensive physicochemical characterization of the synthesized nanoparticles was performed to determine their structural, morphological, magnetic, and surface properties. The TEM images revealed that single-core IONPs were roughly spherical with an average diameter of $10$ nm, while NFs displayed a flower-like morphology with a diameter of $30$ nm. Additionally, the surface area and porosity of the samples were analyzed using nitrogen physisorption measurements at $77$ K, based on adsorption-desorption isotherms. The superparamagnetic behavior of both IONPs and NFs at room temperature was confirmed using a SQUID magnetometer. Moreover, the induction heating ability of both samples under an alternating magnetic field was studied by specific absorption rate (SAR) measurements. The results showed that SAR values increased with the applied magnetic field $H$, reaching up to $\approx 7.9$ $\mathrm{kA\,m^{-1}}$. Notably, NFs exhibited significantly higher SAR values than single-core IONPs, confirming their potential as efficient nano-heaters for magnetic hyperthermia applications.

Acknowledgements

This work was funded by the EU NextGenerationEU through the Recovery and Resilience Plan for Slovakia under the project No. 09I03-03-V04-00296.

References

[1] Y. Q. Meng et al., “Recent trends in preparation and biomedical applications of iron oxide nanoparticles,” Journal of Nanobiotechnology, vol. 22, no. 1. Springer Science and Business Media LLC, Jan. 08, 2024. https://doi.org/10.1186/s12951-023-02235-0
[2] A. A. Kuznetsov et al., “Multicore-based ferrofluids in zero field: initial magnetic susceptibility and self-assembly mechanisms,” Soft Matter, vol. 19, no. 24. Royal Society of Chemistry (RSC), pp. 4549–4561, 2023. https://doi.org/10.1039/d3sm00440f

Speaker: Dr Iryna Khmara (Institute of Experimental Physics, Slovak Academy of Sciences)

36 Correlation of the Structural and Magnetic Morphology of Nanoparticles

The design of magnetic nanoparticles (MNPs) relies on the precise control of size, shape, and material composition, as these parameters critically influence their properties for applications in technology [1], biomedicine [2], and environmental science. Achieving optimal performance in a specific application requires a deep understanding of how the macroscopic properties of MNPs and their ensembles are governed by their nanoscale structural and magnetic characteristics. However, characterizing the magnetic morphology and internal spin structure of MNPs remains a significant challenge, as conventional macroscopic techniques often lack the spatial resolution required to probe these features accurately. To address these limitations, the magnetic Small-Angle Neutron Scattering technique with incident beam polarization (SANSPOL) has emerged as a powerful tool. SANSPOL enables the resolution of magnetization distributions at the nanometer scale, allowing for the disentanglement of spin disorder effects [3-4] and the distinct magnetization contributions from the core and shell regions in core$\\@$shell nanoparticles [5].

In this work, we investigate the influence of chemical composition on the magnetic structure of manganese (Mn)-doped ferrite MNPs. By systematically varying Mn doping levels in cubically shaped CoFe$_2$O$_4$ nanoparticles synthesized via the thermal decomposition method, we achieved uniform particle sizes and narrow size distributions ($\sigma_{log}<10\%$). We used SANSPOL to investigate the chemical homogeneity and magnetic morphology of the MNPs, revealing variations in surface spin disorder linked to Mn concentration. Additionally, we evaluated the heating performance of the Mn-doped MNPs under an alternating magnetic field to assess their potential for applications such as magnetic hyperthermia. By correlating heating efficiency with structural, chemical, and magnetic properties, we established a comprehensive relationship between composition and performance. This study advances the fundamental understanding of magnetic behavior in Mn-doped ferrite MNPs and provides practical guidelines for optimizing their properties for targeted technological and biomedical applications.

Acknowledgements

The authors thank ISIS Neutron and Muon Source for beamtimes (RB2210159 & RB2310314-1) and acknowledge support from the AMULET project supported by the Ministry of Education, Youth, and Sports of the Czech Republic (CZ.02.01.01/00/22_008/0004558), and co-funded by the EU.

References

[1] P. Bender et al., “Relating Magnetic Properties and High Hyperthermia Performance of Iron Oxide Nanoflowers,” The Journal of Physical Chemistry C, vol. 122, no. 5. American Chemical Society (ACS), pp. 3068–3077, Jan. 26, 2018. https://doi.org/10.1021/acs.jpcc.7b11255
[2] A. Lak et al., “Embracing Defects and Disorder in Magnetic Nanoparticles,” Advanced Science, vol. 8, no. 7. Wiley, Feb. 15, 2021. https://doi.org/10.1002/advs.202002682
[3] D. Zákutná et al., “Field Dependence of Magnetic Disorder in Nanoparticles,” Physical Review X, vol. 10, no. 3. American Physical Society (APS), Jul. 24, 2020. https://doi.org/10.1103/physrevx.10.031019
[4] M. Gerina et al., “Size dependence of the surface spin disorder and surface anisotropy constant in ferrite nanoparticles,” Nanoscale Advances, vol. 5, no. 17. Royal Society of Chemistry (RSC), pp. 4563–4570, 2023. https://doi.org/10.1039/d3na00266g
[5] D. Zákutná et al., “Magnetic Coupling in Cobalt-Doped Iron Oxide Core–Shell Nanoparticles: Exchange Pinning through Epitaxial Alignment,” Chemistry of Materials, vol. 35, no. 6. American Chemical Society (ACS), pp. 2302–2311, Mar. 09, 2023. https://doi.org/10.1021/acs.chemmater.2c02813

Speaker: Dr Dominika Zákutná (Department of Inorganic Chemistry, Faculty of Science, Charles University)

37 Directional Relaxation of Stress-Induced Anisotropy of Crystal Lattice in VITROPERM-800

Annealing of amorphous alloy Vitroperm-$800$ in the form of thin ribbons under tensile stress is very effective way of achieving huge value of magnetic anisotropy, which may well exceed the value of magneto-crystalline constant ($8$ kJ/m$^3$) of Fe-Si crystalline phase [1]. As a result of such thermo-mechanical treatment ribbons reveal perfectly linear hysteresis loop with constant slope (permeability) which can be controlled by applied stress. It has been shown in our recent work [2] that such stress induced anisotropy (SIA) is because Fe$_3$Si nanocrystalline grains growing in the tensile direction have a higher value of the lattice spacing as in case of transversal direction, where opposite behavior is seen. Furthermore it was demonstrated that the strain partitioning among different Bragg reflections of Fe$_3$Si phase is not even, and the magnitude of the SIA for a given set of Bragg reflections is inversely proportional to its Young’s modulus $E_{hkl}$.

Acknowledgements

This study was funded by the EU NextGenerationEU through the Recovery and Resilience Plan for Slovakia under the project No. 09I03-03-V03-00034.

References

[1] G. Herzer et al., “Magnetic properties of nanocrystalline FeCuNbSiB with huge creep induced anisotropy,” Journal of Physics: Conference Series, vol. 266. IOP Publishing, p. 012010, Jan. 01, 2011. https://doi.org/10.1088/1742-6596/266/1/012010
[2] D. Yudina et al., “Structural aspects of stress-induced magnetic anisotropy in Fe-based nanocrystalline alloy,” Journal of Alloys and Compounds, vol. 960. Elsevier BV, p. 171011, Oct. 2023. https://doi.org/10.1016/j.jallcom.2023.171011

Speaker: Dr Vladimír Girman (Pavol Jozef Šafárik University in Košice, Faculty of Science, Institute of Physics)

38 Dual-Point Temperature Sensing in Single Glass-Coated Microwire

Microwire sensing technology offers unique capabilities, including the ability to measure temperature at two distinct points using a single sensor without repositioning. This dual-point measurement is based on domain wall propagation from both ends of the glass-coated microwire, as the switching field value is influenced by the local temperature at the de-pinning centre, where the domain wall motion begins [1].

The domain structure of glass-coated magnetically bistable microwires can be simplified into three domains separated by two domain walls. The closure domain expands during remagnetization while the corresponding domain wall propagates along the microwire [2]. A temperature difference between the microwire's ends results in varying switching field values required for re-polarization.

A magnetic field gradient with decreasing intensity along the microwire’s axis must be established to enable effective measurement, requiring two excitation coils or a single coil with adjustable positioning. However, only one sensing coil is sufficient to detect the microwire’s response, making this approach efficient for contactless thermal sensing applications.

Acknowledgements

This work was partially supported by the projects APVV-16-0079 and VEGA-1/0180/23.

References

[1] V. Zhukova et al., “Review of Domain Wall Dynamics Engineering in Magnetic Microwires,” Nanomaterials, vol. 10, no. 12. MDPI AG, p. 2407, Dec. 01, 2020. https://doi.org/10.3390/nano10122407
[2] M. Al Ali et al., “Application of bistable glass-coated microwire for monitoring and measuring the deformations of metal structural members,” Measurement, vol. 208. Elsevier BV, p. 112458, Feb. 2023. https://doi.org/10.1016/j.measurement.2023.112458

Speaker: Dr Ladislav Galdun (RVmagnetics a.s., Nemcovej 30, 04001 Kosice, Slovakia)

39 Effect of Dimensional Parameters on the Magnetic Performance of CoFe$_2$O$_4$ Nano-cubes for Magnetic Hyperthermia

Superparamagnetic iron oxide nanoparticles (SPIONs), particularly Fe$_3$O$_4$, are among the most extensively studied magnetic nanoparticles (MNPs) due to their high biocompatibility and biodegradability, making them highly suitable for biomedical applications such as magnetic resonance imaging (MRI). While SPIONs have demonstrated promising heating capabilities in magnetic hyperthermia, particularly in prostate cancer therapy, their magnetic response under specific conditions—such as varying distances from an external magnetic field, concentration in tumor tissue, and stability in physiological environments—may not always be optimal [1]. To enhance their performance and adapt them to specific biomedical applications, various modification strategies have been explored.

One of the most effective modification approaches involves altering the chemical composition through cation substitution. Partial replacement of Fe atoms with elements such as Mn, Co, or Ni leads to the formation of spinel ferrites with tunable physicochemical properties. By adjusting the cation distribution within the spinel sublattices, the magnetic characteristics of these nanosystems can be fine-tuned through super-exchange interactions. In addition to compositional modifications, strategies such as controlling nanoparticle shape, size, and surface properties further enhance their magnetic performance. These modifications significantly affect key magnetic parameters, particularly anisotropy and coercivity, which are crucial for improving hyperthermia efficiency.

CoFe$_2$O$_4$ nanocubes in three different size modifications ($10$, $13$, and $17$ nm) were prepared by thermal decomposition and investigated to analyze the impact of size variation on their magnetic properties. SQUID magnetometry was used to examine the magnetic properties of the systems by measuring $M$(H) and $M$(T) curves in both Zero-Field Cooling (ZFC) and Field Cooling (FC) regime. The collected data were then analyzed using appropriate models to investigate the overall magnetic behavior of the systems. From this analysis, values for anisotropy, coercivity, and saturation magnetization were extracted. The results were evaluated for the potential use of these nanoparticles in magnetic hyperthermia. In addition to magnetic properties, the structure of the MNPs was examined using TEM/SEM microscopy, and XRD analysis. Based on the obtained results, these systems show promising potential for application in magnetic hyperthermia.

Acknowledgements

Funded by the EU NextGenerationEU through the Recovery and Resilience Plan for Slovakia under the project No. 09I03-03-V04-00177 and supported by the Slovak Research Agency under the contracts: APVV-20-0512 and VEGA1/047/25.

References

[1] C. Caizer, “Magnetic/Superparamagnetic Hyperthermia as an Effective Noninvasive Alternative Method for Therapy of Malignant Tumors,” Nanotheranostics. Springer International Publishing, pp. 297–335, 2019. https://doi.org/10.1007/978-3-030-29768-8_14

Speaker: Daniela Mačáková (Pavol Jozef Šafárik University in Košice, Faculty of Science, Institute of Physics)

40 Electrophysical Properties of Magnetic Composites With Ferrites and Nanocarbon

Polymer composites with inorganic fillers are highly valued for their unique properties and applications in areas such as protective systems, permanent magnets, magnetic delivery, microelectronics, and biomedicine. Recent studies suggest that using combined fillers, like nanocarbon and inorganic particles (e.g., magnetic oxides, barium hexaferrite, and other ferrites [1]), is a promising approach for developing advanced materials with exceptional properties.

In this work, composite materials based on epoxy resin (Larit$285$) with a combined filler of graphite nanoplates (GNP) /ferrites (CuFe$_2$O$_4$, NiFe$_2$O$_4$, and CoFe$_2$O$_4$) and multiwalled carbon nanotubes (MWCNT) /ferrites were manufactured and investigated. The content of nanocarbon varied from $2$ wt.$\%$ to $5$ wt.$\%$, and ferrites content was $20$ wt.$\%$. The electrical resistivity of the investigated composites was measured by the standard methods in DC mode at $T=77-293$ K; the frequency dependencies of microwave permittivity $\varepsilon(f)$ and permeability $\mu(f)$ were measured with E$4991$B Impedance Analyzer (Keysight Technologies, USA) in the frequency range $1-500$ MHz.

The experimental temperature dependences of the electrical resistance of nanocarbon/ferrite epoxy composites are explained in terms of the change in the temperature coefficient of resistance (TCR), the nature of which is determined by the change in the electrical transport mechanism in the material:
$$ TCR =\frac{1}{R}\frac{dR}{dT}. $$ The investigated composites GNP/ferrite and MWCNT/ferrite are characterized by different types of temperature dependence of electrical resistance, with a positive or a negative TCR, depending on which of the temperature-dependent processes are predominant. AC electrical conductivity for investigated composites was determined as: $$ \sigma_{AC}(f) = 2\pi f\varepsilon_{0}\varepsilon_{r}^{\prime}$$ The differences in the obtained $\varepsilon(f)$, $\mu(f)$, $\sigma_{AC}(f)$ dependences for nanocarbon/ferrite composites with different types of fillers are discussed.

Acknowledgments

The work was funded by the Ministry of Education and Science of Ukraine, grants 24BF051-01M (0124U001654), 24BF051-04, and by the National Research Foundation of Ukraine NRFU2023-03/193.

References

[1] R. Kumar et al., “Recent progress on carbon-based composite materials for microwave electromagnetic interference shielding,” Carbon, vol. 177. Elsevier BV, pp. 304–331, Jun. 2021. https://doi.org/10.1016/j.carbon.2021.02.091

Speaker: Dr Yuliia Mazurenko (Institute of Experimental Physics, Slovak Academy of Sciences)

41 Evolution of Nano-Precipitates and Their Effect on Microstructural Design and Magnetic Properties of Electrical Steel

Electrical steels are Fe-Si alloys with a silicon content typically ranging from 0 to $6.5$ wt$\%$. They belong to soft magnetic materials and are commonly used as core materials in various electromagnetic applications for generating, distributing, and consuming electrical energy. The thin sheets of these steels are classified into Grain-Oriented (GO) and Non-Oriented (NO) electrical steels. GO steels have exceptional microstructures consisting of centimeter-sized grains with the crystal lattice having the so-called Goss orientation $\{110\}$<$001$>, which are manifested by low power losses and high permeability in the rolling direction. Therefore, they are predominantly employed for the transformers with high efficiency. The most desirable $\{110\}$<$001$> crystallographic orientation in GO steel is achieved through abnormal grain growth, forced by the appropriate morphology of secondary phase particles such as MnS, AlN, and MnS+AlN.

NO electrical steels exhibit nearly identical magnetic properties in all directions within the sheet and are primarily used as core materials in rotating equipment. The isotropic magnetic properties can be achieved through the so-called "rotating" cube texture, defined by the $\{100\}$<$0$vw> crystallographic orientation.

In the present work, we introduce an original concept of thermo-chemical treatment for NO silicon steel to achieve a composite microstructure through the cross-section of the steel sheet. The proposed microstructural design ensures a combination of high strength and relevant magnetic properties, making it suitable for the construction of rotor cores in electric and hybrid vehicles. Our approach is based on abnormal grain growth with an appropriate crystallographic orientation, achieved by strain-induced grain boundary migration mechanism in combination with the inhibiting effect of nano-precipitates, primarily distributed in the subsurface region. A layer of coarse-grained microstructure (grain size $\sim 150$ $\mu$m) with a strong cubic $\{100\}$<$0$vw> or Goss $\{110\}$<$001$> crystallographic orientation was obtained in the central part of the steel sheet cross-section. This microstructure provides the desired magnetic properties. Additionally, a fine-grained microstructure (grain size $\sim 15$ $\mu$m), formed by nano-precipitates, was achieved in both sub-surface regions to enhance the mechanical strength. The proposed composite microstructure of NO steel demonstrates magnetic losses of approximately $9$ W/kg, comparable to the magnetic properties of samples processed under conventional industrial conditions. Stress-strain tests show that our samples exhibit a more than $30\%$ increase in tensile strength compared to the same material without a composite microstructure.

Acknowledgements

The work was carried out within the research project funded by the EU NextGenerationEU through the Recovery and Resilience Plan for Slovakia under project No. 09I03-03-V04-00314.

Speaker: Dr Ivan Petryshynets (Institute of Materials Research, Slovak Academy of Sciences)

42 Finite Elements-Based Method of Modeling the Eddy-Current Losses in Ribbon Ring-Shaped Cores With a Gap

Finemet-type alloys are very promising materials for the inductive cores of chokes. The functional properties of such materials produced during the recrystallization of amorphous ribbons can be widely modified by the recrystallization parameters. Moreover, due to the small thickness of the nanocrystalline ribbon, the eddy current losses might be controlled by the changes in the effective conductivity of the core, determined by the efficiency of the contact between the layers of the ribbon ring core.

On the other hand, a very promising method of controlling the magnetodynamic parameters of the inductive cores of chokes is introducing the gaps in the magnetic circuit of the ribbon ring core [1]. Such gaps increase the core’s reluctance as well as cause a magnetic flux fringing effect connected with the spreading out of the magnetic flux lines as they pass through an air gap in a magnetic core. In addition, this effect can be controlled by the changes in the gap width. In addition, it is possible to split one single gap into a series of smaller gaps [2] for better control of the results.

However, an efficient modeling method is necessary for a better understanding and control of both the magnetic flux fringing effect and eddy current losses in one single gap into a series of smaller gaps in the magnetic circuit. This paper presents the results of the investigation on modeling the Finemet-type ribbon ring-shaped core with a double gap. Moreover, the ribbon ring-shaped core was subjected to high-pressure epoxy covering to improve its mechanical stability and increase the electrical separation among the ribbon layers.

Investigation was carried out on the base of open source software. A modeling toolchain covering NETGEN tetrahedral mesher, ELMER FEM solver, and GNU-OCTAVE control was created. The paper presents the modeling results compared to the experimental measurements and guidelines for the efficient finite elements-based modeling of the magnetization characteristics and losses in nanocrystalline ribbon ring-shaped cores with single or a series of gaps.

Acknowledgements

This work was supported by the National Centre for Research and Development under European Funds for a Modern Economy (FENG SMART). The project title: "Advanced design and production of hybrid cores for chokes in high-speed motor filters operating at higher frequencies using numerical analysis and innovative process improvement technologies", project number: FENG.01.01-IP.01-A00H/23.

References

[1] D. I. Zaikin et al., “An Air-Gap Shape Optimization for Fringing Field Eddy Current Loss Reductions in Power Magnetics,” IEEE Transactions on Power Electronics, vol. 34, no. 5. Institute of Electrical and Electronics Engineers (IEEE), pp. 4079–4086, May 2019. https://doi.org/10.1109/tpel.2018.2868289
[2] G. Calderon-Lopez et al., “Mitigation of Gap Losses in Nanocrystalline Tape-Wound Cores,” IEEE Transactions on Power Electronics, vol. 34, no. 5. Institute of Electrical and Electronics Engineers (IEEE), pp. 4656–4664, May 2019. https://doi.org/10.1109/tpel.2018.2863665

Speaker: Prof. Roman Szewczyk (Institute of Metrology and Biomedical Engineering. Warsaw University of Technology)

43 Grain Size Determination using XRD Line Profiles via Iterative Convolution

Understanding and controlling the microstructure of soft magnetic nanocrystalline materials is crucial since it strongly influences the material's magnetic properties, such as coercivity, permeability, and saturation magnetization. By meticulously tailoring the grain size and size distribution, one can minimize energy losses, optimize performance, and enhance the material's efficiency in various applications, including transformers, inductors, and electric motors. In essence, mastering microstructure paves the way for superior magnetic behavior, enabling advancements in energy-efficient technologies.

X-ray diffraction (XRD) is a powerful and non-destructive technique for characterizing the microstructure of materials. By examining the broadening of diffraction peaks, which occurs due to the finite size of the grains, XRD enables the calculation of grain sizes with high accuracy. This information is crucial for understanding the material's properties and performance, as grain size strongly influences magnetic properties [1].

This work is focused on design and verification of an iterative convolution algorithm that serves to determine the true shape of the diffraction profiles after eliminating the instrumental contribution due to its insufficient angular resolution. The proposed algorithm was verified on synchrotron X-ray diffraction patterns acquired on the Vitroperm alloy. Test specimens with two different nanocrystalline states were prepared by isothermal annealing of the amorphous precursor at $520$ °C for $30$ and $150$ minutes. The profiles of Bragg peaks, adjusted for instrumental broadening, were used to determine the average grain sizes of the nanocrystalline Fe$_3$Si phase. Results obtained from a novel iterative convolution algorithm are promising, demonstrating some advantages over deconvolution-based techniques.

Acknowledgements

This study was funded by the EU NextGenerationEU through the Recovery and Resilience Plan for Slovakia under the project No. 09I03-03-V03-00034.

References

[1] G. Herzer, “Nanocrystalline soft magnetic materials,” Journal of Magnetism and Magnetic Materials, vol. 157–158. Elsevier BV, pp. 133–136, May 1996. https://doi.org/10.1016/0304-8853(95)01126-9

Speaker: Mr Peter Dubecký (Pavol Jozef Šafárik University in Košice, Faculty of Science, Institute of Physics)

44 High Temperature Measurement Using Glass Coated Bistable MicroWires

Accurate high-temperature measurement is a critical challenge in various industrial applications, including metallurgy, aerospace, and power generation. Traditional thermocouples and resistance temperature detectors (RTDs) suffer from drift, material degradation, and signal loss at extreme temperatures, necessitating alternative solutions for reliable temperature monitoring. In this work, we explore the potential of glass-coated bistable microwires [1] as a novel method for contactless temperature sensing in environments reaching up to $500$ °C.

Bistable ferromagnetic microwires exhibit a sharp magnetization switching behavior, which is highly sensitive to external temperature variations. By leveraging the temperature dependence of their switching field, we develop a contactless measurement technique that enables real-time monitoring of high-temperature processes. Protective glass coating enhances thermal stability and prevents oxidation, extending the sensor's operational lifetime compared to conventional alternatives [2].

Experimental results demonstrate that the microwires maintain their bistable behavior and provide a measurable and reproducible signal up to $500$ °C. This technology offers a non-invasive, wireless, and durable alternative for high-temperature sensing in industrial settings where conventional probes fail. The proposed method paves the way for innovative, cost-effective solutions for real-time temperature monitoring in extreme environments.

Acknowledgements

This work was partially supported by the projects APVV-16-0079 and VEGA-1/0180/23

References

[1] R. Varga et al., “Magnetically Bistable Microwires: Properties and Applications for Magnetic Field, Temperature, and Stress Sensing,” Springer Series in Materials Science. Springer International Publishing, pp. 169–212, 2017. https://doi.org/10.1007/978-3-319-49707-5_8
[2] P. Klein et al., “Bistable FeCoMoB microwires with nanocrystalline microstructure and increased Curie temperature,” Journal of Physics D: Applied Physics, vol. 43, no. 4. IOP Publishing, p. 045002, Jan. 12, 2010. https://doi.org/10.1088/0022-3727/43/4/045002

Speaker: Simona Findrikova (UPJS, RVmagnetics a.s.)

45 Highly Anisotropic Magnetic CoFe$_2$O$_4$ Nanoparticles in Various Shapes as Magneto-Thermal Agents

Over the past decade, magnetic nanoparticles (MNPs) have been extensively investigated for their potential application in magnetic particle hyperthermia, a promising strategy in cancer treatment due to its targeted and localized effects [1]. This approach utilizes MNPs as agents that facilitate the conversion of electromagnetic energy from an alternating magnetic field into heat. The effectiveness of this technique depends on the selection of suitable magnetic nanoparticles, which must meet specific criteria related to biocompatibility, cytotoxicity, morphology, and magnetic properties. Additionally, several key parameters influence the heating efficiency of MNPs in an AC magnetic field, including saturation magnetization, anisotropy constant, coercivity, and magnetic moment magnitude.

Magnetic CoFe$_2$O$_4$ nanoparticles, synthesized via thermal decomposition, were prepared in three distinct morphological forms: spherical and cubic particles of approximately $10$ nm in size, as well as star-shaped nanoparticles with an average size of $16$ nm. These highly crystalline nanostructures were investigated to assess their structural, magnetic, and magneto-thermal properties. X-ray diffraction confirmed the formation of the cobalt ferrite spinel structure, while transmission electron microscopy verified shape variations induced by synthesis conditions. X-ray photoelectron spectroscopy analysis provided insights into the elemental composition, particularly the Co:Fe atomic ratio within the spinel lattice. A detailed analysis of the magnetic properties was performed using SQUID magnetometry through measurements of magnetization curves $M(H)$ and temperature-dependent $M(T)$ curves in the ZFC/FC regime. This investigation revealed high values of magnetic anisotropy and coercivity in both cubic and star-shaped nanoparticles, which are critical for efficient heating in magnetic particle hyperthermia. Additionally, the influence of nanoparticle shape on these key magnetic parameters was studied, as variations in morphology can significantly impact their magnetothermal performance.

Acknowledgements

Funded by the EU NextGenerationEU through the Recovery and Resilience Plan for Slovakia under the project No. 09I03-03-V04-00177 and supported by the Slovak Research Agency under the contracts: APVV-20-0512 and VEGA1/047/25.

References

[1] X. Liu et al., “Comprehensive understanding of magnetic hyperthermia for improving antitumor therapeutic efficacy,” Theranostics, vol. 10, no. 8. Ivyspring International Publisher, pp. 3793–3815, 2020. https://doi.org/10.7150/thno.40805

Speaker: Dr Ľuboš Nagy (Pavol Jozef Šafárik University in Košice, Faculty of Science, Institute of Physics)

46 In-situ XRD Observation of Stress Induced Anisotropy in Vitroperm $800$

Fe-based nanocrystalline alloys exhibit distinctive soft magnetic properties, which are obtained through a heat treatment process. This treatment partially devitrifies the amorphous precursor, leading to the development of a microstructure composed of ultra-fine grains, smaller than $30$ nm, embedded within a remaining amorphous matrix [1]. The application of heat treatment combined with tensile deformation offers a promising method to further optimize microstructure, resulting in enhanced magnetic properties [2]. The induced magnetic anisotropy energy is directly proportional to the stress applied during annealing and can reach values in the range of several thousand J/m$^3$, two orders of magnitude greater than the typical field-induced anisotropies. These robust and precisely controlled anisotropies are particularly valuable for applications such as magnetic energy storage cores, which demand low permeability, typically around a few hundred. Previous research indicates that the stress-induced anisotropy (SIA) in Fe-based alloys stems from the structural anisotropy of Fe$_3$Si nanocrystalline grains [3,4].

This study builds upon previous research by providing direct in-situ X-ray diffraction (XRD) observations of SIA in nanocrystalline Fe-based alloy (Vitroperm $800$). Melt spun amorphous ribbons were subjected to tensile loading at elevated temperatures and temporal evolution of the SIA formation was observed using in-situ XRD experiments at the P$02.1$ beamline of the synchrotron storage ring PETRA III at DESY Hamburg. These studies demonstrate how tensile stress during annealing influences the lattice strain of cubic Fe$_3$Si phase, offering a more detailed understanding of the mechanisms driving SIA.

Acknowledgements

This research was supported by the Grant Programme for SAS PhD students, project no. APP0626, funded by the Slovak Academy of Sciences. Funded by the EU NextGenerationEU through the Recovery and Resilience Plan for Slovakia under the project No. 09I03-03-V03-00034.

References

[1] Y. Yoshizawa et al., “New Fe-based soft magnetic alloys composed of ultrafine grain structure,” Journal of Applied Physics, vol. 64, no. 10. AIP Publishing, pp. 6044–6046, Nov. 15, 1988. https://doi.org/10.1063/1.342149
[2] G. Herzer et al., “Magnetic properties of nanocrystalline FeCuNbSiB with huge creep induced anisotropy,” Journal of Physics: Conference Series, vol. 266. IOP Publishing, p. 012010, Jan. 01, 2011. https://doi.org/10.1088/1742-6596/266/1/012010
[3] M. Ohnuma et al., “Direct evidence for structural origin of stress-induced magnetic anisotropy in Fe–Si–B–Nb–Cu nanocrystalline alloys,” Applied Physics Letters, vol. 83, no. 14. AIP Publishing, pp. 2859–2861, Oct. 06, 2003. https://doi.org/10.1063/1.1615672
[4] D. Yudina et al., “Structural aspects of stress-induced magnetic anisotropy in Fe-based nanocrystalline alloy,” Journal of Alloys and Compounds, vol. 960. Elsevier BV, p. 171011, Oct. 2023. https://doi.org/10.1016/j.jallcom.2023.171011

Speaker: Ms Ravneet Kaur (Pavol Jozef Šafárik University in Košice, Faculty of Science, Institute of Physics)

47 Influence of the Distribution of Electroinsulator on the Magnetic Properties of NiFeMo Based Soft Magnetic Composites

Soft magnetic composites (SMCs), which have isotropic ferromagnetic behavior, high saturation magnetization, high permeability, and relatively low core loss, have been regarded as key components of electromagnetic systems in higher frequency range [1]. This work focuses on investigating the effect of adding Al$_2$O$_3$ or h-BN as a layer keeping the electric insulation of the NiFe-based SMC structure. Soft magnetic composites based on NiFeMo powder particles encapsulated in Al$_2$O$_3$ or h-BN matrix are prepared by powder metallurgy process followed by compaction. The structure and various magnetic properties related to their soft magnetic performance are analyzed. Four samples prepared are with volume ratio ($98.8:1.2$ and $95:5$) of the mixture of NiFeMo and Al$_2$O$_3$ or h-BN.

The most important properties studied here are complex permeability and total energy loss. Further important characteristics are initial relative permeability, maximum relative permeability and coercivity. As both the electroinsulators contribute to the entire electrical resistivity, the resulting composites possess improved electromagnetic performance. This is fulfilled by electrically insulating coating on the surface of powder particles, limiting the eddy current paths into the cross-section of isolated particles. The magnetic losses in the frequency range from DC to $50$ kHz on ring-shaped samples are shown to be suppressed thanks to the lower eddy currents. The real part of complex permeability keeps a constant value until higher frequencies in comparison with NiFeMo sample. The peak of imaginary part of relative complex permeability is shifted from $5$ kHz for NiFeMo to $10.5$ kHz for the sample with $1.2\%$ and to $80$ kHz for the sample with $5\%$ Al$_2$O$_3$ content. Position of peaks for samples with h-BN are at significantly higher values, $250$ kHz for sample with $1.2\%$ and 400 kHz for sample with $5\%$ h-BN content. Herein, the imaginary components shift with rising electric insulation amounts, corresponding with the measured electrical resistivity values. Therefore, the use of the h-BN as an insulating layer with more uniform distribution in soft magnetic composites has promising potential in meeting requirements in the high-frequency range.

Acknowledgements

This work has been supported by the Scientific Grant Agency of the Ministry of Education, Science, Research & Sport of the Slovak Republic and the Slovak Academy of Sciences (VEGA 1/0132/24, and VEGA 1/0403/23) and by the EU NextGenerationEU through the Recovery and Resilience Plan for Slovakia under the project No. 09I03-03-V03-00034.

References

[1] E. A. Périgo et al., “Past, present, and future of soft magnetic composites,” Applied Physics Reviews, vol. 5, no. 3. AIP Publishing, p. 031301, Sep. 2018. https://doi.org/10.1063/1.5027045

Speaker: Dr Ján Füzer (Pavol Jozef Šafárik University in Košice, Faculty of Science, Institute of Physics)

48 Investigating Magnetic Properties of Octapod-Shaped Magnetic Nanoparticles via AC Susceptibility

In recent years, nanoparticles and their applications have attracted significant interest from biomedical researchers. Nanoparticles smaller than $100$ nm exhibit unique properties, including high surface-to-volume ratios, high reactivity, enhanced thermal conductivity, and tunable optical characteristics. These features make them highly useful across various fields, particularly in biomedical applications. Key applications include magnetic resonance imaging (MRI), drug or gene delivery systems, and magnetic hyperthermia, where nanoparticles serve as a heat source.

Interparticle interactions can significantly influence superparamagnetic relaxation. Furthermore, interparticle interactions can modify the spin structure of nanoparticles. An assembly of nanoparticles coupled by sufficiently weak inter-particle interactions exhibits superparamagnetic behaviour, whereas stronger interactions in densely packed systems can stabilise a superspin glass or superferromagnetic state. One of the most effective methods to gain deeper insight into the nature of these interactions and estimate their strength is the analysis of AC magnetic susceptibility.

Magnetic measurements were performed on a commercial superconducting quantum interference device (SQUID) magnetometer (Quantum Design MPMS3) in the temperature interval from $2$ K to $300$ K at various frequencies of the alternating magnetic field. The complex AC magnetic susceptibility,
$$\chi=\chi^{\prime}+\chi^{\prime\prime}$$ consists of $\chi^{\prime}$, which represents the in-phase (real) component of the AC susceptibility, and $\chi^{\prime\prime}$, which corresponds to the out-of-phase (imaginary) component. Experimental data were analysed using models that assume different strengths of interparticle interactions, including the Néel-Arrhenius and Vogel-Fulcher laws, as well as critical slowing-down analysis. The results provide an estimation of interaction strength and reveal crucial aspects of magnetic dynamics in nanoparticle systems.

Acknowledgements

This work was supported by the Slovak Research and Development Agency under the contracts No. APVV-20-0512 and VEGA 1/0470/25.

References

[1] A. V. B. Pinheiro et al., “Exchange bias and superspin glass behavior in nanostructured CoFe2O4-Ag composites,” Journal of Magnetism and Magnetic Materials, vol. 497. Elsevier BV, p. 165940, Mar. 2020. https://doi.org/10.1016/j.jmmm.2019.165940

Speaker: Žaneta Fabriciová (Pavol Jozef Šafárik University in Košice, Faculty of Science, Institute of Physics)

49 Investigation of Structural Heterogeneity in Soft Magnetic Materials Formed by Hot Powder Compaction

Soft magnetic materials formed by hot powder powder compaction are a distinct class with significant application potential. They possess exceptional magnetic properties, such as low core losses, high permeability, and $3$-D isotropic magnetic behavior. The shape and size distribution of the powder particles, along with the processing conditions such as compaction temperature and pressure, determine the final density, mechanical, and magnetic properties of the compacted soft magnetic material. Furthermore, the shape of the particles and the level of porosity in compacted materials significantly impact their magnetic behavior. The surfaces of the ferromagnetic particles within the porous structure of powder compacts create internal demagnetizing fields, which negatively impact the magnetic permeability. These demagnetizing fields diminish the internal magnetic field within the compacted material, leading to a reduction in its permeability. Rough surfaces also hinder the movement of domain walls in ferromagnetic materials.

In this study, two ring-shaped specimens were prepared by hot powder compaction. Resulting specimen had outer and inner diameters of $24$ mm and $18$ mm, respectively, with a height of $3$ mm. The compaction was performed at a pressure of $700$ MPa for $3$ minutes at a temperature of $400$ °C. The powder used in compaction was prepared by: (i) grinding pure iron granulates in a planetary ball mill, (ii) extracting a size fraction of $63-125$ $\mu$m by sieving, and (iii) annealing for $90$ minutes at $400$ °C. The first ring-shaped sample was prepared using the initial powder, while the second sample was prepared with powder that underwent an additional surface smoothing treatment using grinding paper with SiC grit of grade P$1200$. Microstructure of the compacted materials was examined using X-ray absorption tomography with a Zeiss XRadia $610$ Versa. The variation in the atomic structure of compacted materials was analyzed by conducting a line scan in transmission geometry across the sample width using a well-focused ( $9\;\mu$m $\times 2\;\mu$m) high-energy ($67.8$ keV) photon beam at the P$21.2$ synchrotron beamline at PETRA III in DESY, Hamburg, Germany.

Acknowledgements

This study was funded by the EU NextGenerationEU through the Recovery and Resilience Plan for Slovakia under the project No. 09I03-03-V03-00034. We acknowledge DESY (Hamburg, Germany), a member of the Helmholtz Association HGF, for the provision of experimental facilities. Parts of this research were carried out at PETRA III and we would like to thank U. Linenert for assistance in using P21.2 beamline.

Speaker: Prof. Peter Kollár (Pavol Jozef Šafárik University in Košice, Faculty of Science, Institute of Physics)

50 Investigation of Structure-Property Relationships in Fe-Based Nanocrystalline Alloy

Fe-based alloys, characterized by their unique nanocrystalline structure, exhibit remarkable soft magnetic properties such as high relative permeability ($>10^{5}$), high saturation magnetization ($>1.0$ T), low coercivity and almost zero magnetostriction [1], making them ideal candidates for a wide range of technological applications, such as transformer cores, inductors, and magnetic sensors. All of these exceptional magnetic properties arise from their unique microstructure characterized by ultrafine grains with a relatively narrow size distribution ($10-50$ nm), which are homogeneously dispersed in the residual amorphous matrix [2].

This article is devoted to the study of the Fe$_{73.5}$Cu$_{1}$Nb$_{3}$Si$_{15.5}$B$_{7}$ alloy and the correlation of its nanocrystalline microstructure with the resulting magnetic properties (mainly coercivity). Subtle changes in the microstructure were induced by a series of isothermal annealing with different annealing times and temperatures. These microstructural changes were investigated using X-ray diffraction, transmission electron microscopy, small-angle X-ray scattering and magnetic measurements. The magnetic properties of all series of isothermally annealed samples were investigated using Koerzimat, Mossbauer spectroscopy and ferromagnetic resonance. It is shown that a series of isothermal annealing causes subtle changes in the microstructure of the nanocrystalline material, which are visible in course of coercivity and by means of FMR measurements. SAXS proved to be a sensitive method for describing thermally induced changes in the microstructure (especially particle size and distribution) with respect to a wide range of length scales involved.

Acknowledgments

This study was funded by the EU NextGenerationEU through the Recovery and Resilience Plan for Slovakia under the project No. 09I03-03-V03-00034.

References

[1] P. R. Roach et al., “Spin structure of solid 3He below 1 mK neutron diffraction,” AIP Conference Proceedings, vol. 103. AIP, pp. 82–82, 1983. https://doi.org/10.1063/1.34214
[2] G. Herzer, “Nanocrystalline soft magnetic materials,” Journal of Magnetism and Magnetic Materials, vol. 157–158. Elsevier BV, pp. 133–136, May 1996. https://doi.org/10.1016/0304-8853(95)01126-9

Speaker: Dr Daria Yudina (Pavol Jozef Šafárik University in Košice, Faculty of Science, Institute of Physics)

51 Investigations of Magnetic Properties of Nanoribbon Arrays Based on Co and Cu

The development of spintronic devices has attracted a lot of interest due to their advantages in electronics, including energy non-volatility, low power consumption and high data processing speed. Currently, a large number of various magnetic materials for spintronics devices have been investigated. Nanofabrication methods provide an opportunity to reduce the dimensionality of such materials and gain new insights into their properties. Electron-beam lithography combined with various condensation methods enables the fabrication of novel magnetic nanostructures with controlled anisotropic properties, high magnetization stability, and the capability for effective control of magnetic states. Thus, the goal of our work is to fabricate one-dimensional arrays of Co- and Cu-based nanoribbons, systematically investigate their magnetic properties, and evaluate their applications in spintronics devices.

Nanoribbon arrays based on cobalt and copper nanoparticles were fabricated using a combination of electron-beam lithography and electrochemical deposition techniques. Analysis of the phase composition and crystal structure of arrays of Co$_{75}$Cu$_{25}$-based nanoribbons showed the formation of Co (Cu) solid solution with an average grain size of about $8$ nm. Annealing to $750$ K in Ar/H$_2$ atmosphere for $20$ min does not significantly affect the phase composition, but leads to an increase in the average crystallite size up to $45$ nm.

The study of nanoribbon arrays by the MFM method has shown the presence of a bamboo-like domain structure, the appearance of which is associated with longitudinal magnetic anisotropy. This structure arises due to the orientation of grains along the ribbon and a small number of grain boundaries in the transverse direction. This reduces the number of domain walls forming elongated domains, which decreases the magnetostatic interaction energy. The presence of longitudinal magnetic anisotropy is confirmed by studies of magnetic properties at two orientations of arrays of nanoribbons relative to the magnetic field: parallel and perpendicular. A decrease in the coercivity from $366$ Oe to $269$ Oe and in the blocking temperature from $191$ K to $168$ K is observed in the transition from parallel to perpendicular orientation. Furthermore, EPR studies revealed significant differences in the spectra and spin dynamics in the parallel and perpendicular orientations. Annealing leads to a weakening of the longitudinal magnetic anisotropy due to recrystallization processes. The bamboo-like domain structure disappears, and the differences in magnetic properties in the two orientations of the magnetic field become less pronounced.

Acknowledgments

This work has been funded by the EU NextGenerationEU through the Recovery and Resilience Plan for Slovakia under the project No. 09I03_03_V0400179. V. Komanický acknowledges the financial support provided under the APVV-20-0324 project.

Speaker: Dr Serhii Vorobiov (Department of condensed matter physics, Faculty of Science, P.J. Šafárik University, Park Angelinum 9, 041 54 Košice, Slovak Republic)

52 Ligand Exchange Effect on Stabilization and Magnetic Properties of Cobalt-Ferrite Nanoparticles

Cobalt-ferrite (CoFe$_2$O$_4$) nanoparticles (NPs) are valued for their strong magnetism, chemical stability, and mechanical strength, making them useful in multiple fields. In biomedicine, they enable targeted drug delivery, hyperthermia cancer treatment, and MRI contrast enhancement. To employ them in various applications, covering their surface with some specific layer is often inevitable. The layer usually facilitates several functions simultaneously. It prevents agglomeration, promotes the stability of the NP dispersion, provides biocompatibility, and enables further modification by a specific ligand.

Using the thermal decomposition method, we have prepared monodispersed CoFe$_2$O$_4$ NPs of average size $12$ nm as documented by transmission electron microscopy, scanning electron microscopy, and X-ray powder diffraction. For their employment in biomedical applications (magnetic hyperthermia), hydrophobic oleic acid (OA) that covers the surface of as-prepared NPs has to be replaced by a hydrophilic ligand. For this purpose, we have exchanged OA with polyacrylic acid (PAA), obtaining excellent stability of the NP dispersion in water (documented by dynamic light scattering). Further experimental methods (X-ray photoelectron spectroscopy, zeta potential measurements) have also reconfirmed the successful ligand exchange process. However, it is known that bonding some ligands may significantly affect the NP surface layer and, consequently, its magnetic performance. In this context, we have examined and compared the magnetic properties of the as-prepared system (CoFe$_2$O$_4\\@$OA) and the system after ligand exchange (CoFe$_2$O$_4\\@$PAA). The analysis of experimental data obtained in the temperature range of $5-300$ K and applied fields up to $5$ T evidenced that replacing OA with PAA has no deleterious impact on the magnetic characteristics of the prepared NPs.

Acknowledgements

This work was supported by the Slovak Research and Development Agency under the contracts No. APVV-20-0512 and VEGA 1/0470/25, by the Slovak Academic Information Agency and by the EU NextGenerationEU through the Recovery and Resilience Plan for Slovakia under project No. 09I03-03-V04-00325.

Speaker: Dr Pavol Hrubovčák (Pavol Jozef Šafárik University in Košice, Faculty of Science, Institute of Physics)

53 Magnetic Influence on Thermoelectric Properties of Fe$_2$TiAl Heusler Alloy

Thermoelectric materials are a unique class of materials that enable the conversion of heat (e.g., waste heat) into electric energy, making them crucial for energy harvesting. The most well-known thermoelectric materials are the semiconductors, such as Bi$_2$Te$_3$, widely used for their well-defined thermoelectric properties [1]. However, their preparation is both expensive and time-consuming.

The performance of thermoelectric materials is defined by three physical quantities – the Seebeck coefficient, electrical conductivity, and thermal conductivity. Ideally, the Seebeck coefficient and electrical conductivity should be as high as possible, while thermal conductivity should be minimised. In conventional semiconducting materials, charge carrier diffusion has the most significant impact in determining those properties [2]. However, when the value of the Seebeck coefficient decreases, the value of electrical conductivity increases, creating a challenge in band-engineering of the semiconducting materials, as both values should be maximised.

Recently, new promising materials for thermoelectric applications are being studied – magnetic metals. While charge carrier diffusion remains a fundamental mechanism in all thermoelectric materials, magnetic metals exhibit additional processes – spin fluctuation and the magnon-drag effect – which influence thermoelectric properties without directly affecting charge carriers [2]. This creates an opportunity to enhance thermoelectric performance purely through the material’s magnetic properties.

One such magnetic metal exhibiting thermoelectric properties represents the Heusler alloy Fe$_2$TiAl [3]. Its main benefits include the cost of individual elements and fast preparation via the arc-melting method. This study will focus on optimising the composition of Fe$_2$TiAl to achieve desirable thermoelectric properties at specific temperatures while investigating the contribution of the material’s magnetic behaviour to thermoelectric performance.

Acknowledgements

This work was supported by the projects APVV-16-0079, VEGA-1/0180/23, VEGA-1/0407/24, and University Science Park TECHNICOM for Innovation Applications Supported by Knowledge Technology– II- Phase, ITMS: 313011D232., supported by the Research & Development Operational Programme funded by the ERDF.

References

[1] X. Tang et al., “A comprehensive review on Bi2Te3‐based thin films: Thermoelectrics and beyond,” Interdisciplinary Materials, vol. 1, no. 1. Wiley, pp. 88–115, Jan. 2022. https://doi.org/10.1002/idm2.12009
[2] Z. Gui et al., “Large Improvement of Thermoelectric Performance by Magnetism in Co‐Based Full‐Heusler Alloys,” Advanced Science, vol. 10, no. 28. Wiley, Aug. 04, 2023. https://doi.org/10.1002/advs.202303967
[3] R. O. Suzuki and T. Kyono, “Thermoelectric properties of Fe2TiAl Heusler alloys,” Journal of Alloys and Compounds, vol. 377, no. 1–2. Elsevier BV, pp. 38–42, Sep. 2004. https://doi.org/10.1016/j.jallcom.2004.01.035

Speaker: Samuel Nalevanko (Inst. Phys., Fac. Sci., UPJS, Kosice, Slovakia)

54 Magnetic Morphology of Multishell Nanoparticles

Magnetic nanoparticles (MNPs) and their unique properties are of intense research interest. These nanoscopic materials exhibit complex magnetic behavior, which is essential in the proposed applications, ranging from spintronics and catalysis to biomedicine, where they found their usage as contrast agents in imaging techniques or innovative cancer treatment (hyperthermia) [1]. This led to a substantial investigation, particularly aimed at iron oxide MNPs. However, we present a novel candidate, the $\varepsilon$-Fe$_3$N, possessing unprecedented magnetic properties in bulk form, surpassing classical MNPs of iron oxides. In this contribution, we will present a comprehensive characterization of passivated $\varepsilon$-Fe$_3$N MNPs with a mean particle diameter of $17.2(2)$ nm. The complex magnetic nature of this material was disentangled by probing magnetic scattering fluctuations using the magnetic small-angle scattering with incident beam polarization at the D$33$ instrument at ILL [3]. In summary, we will reveal the radial distribution of nuclear scattering density, expose the magnetic morphology of passivated $\varepsilon$-Fe$_3$N MNPs, unravel magnetization contributions from the magnetic core and shell, and ultimately discuss the resulting magnetic response of presented MNPs.

Acknowledgements

This work was supported by the Czech Science Foundation (22-10035K) and the AMULET project, co-funded by MŠMT and the EU (CZ. 02.01.01/00/22_008/0004558). We also acknowledge the Institut Laue-Langevin for beamtime and financial support.

References

[1] L. M. Bauer et al., “High-performance iron oxide nanoparticles for magnetic particle imaging – guided hyperthermia (hMPI),” Nanoscale, vol. 8, no. 24. Royal Society of Chemistry (RSC), pp. 12162–12169, 2016. https://doi.org/10.1039/c6nr01877g
[2] I. Dirba et al., “Evaluation of Fe-nitrides, -borides and -carbides for enhanced magnetic fluid hyperthermia with experimental study of α″-Fe16N2 and ϵ-Fe3N nanoparticles,” Journal of Physics D: Applied Physics, vol. 56, no. 2. IOP Publishing, p. 025001, Nov. 17, 2022. https://doi.org/10.1088/1361-6463/aca0a9
[3] S. Hricov et al., “Unmasking the Complex Core-Multishell Morphology of Magnetic Nanoparticles.” Institut Laue-Langevin (ILL), 2023. https://doi.org/10.5291/ILL-DATA.DIR-297

Speaker: Štefan Hricov (Faculty of Mathematics and Physics, Charles University)

55 Magnetic Nanoparticles Integrated Into SiO$_2$ Hydrogel: Synthesis, Properties, and Applications

Silica (SiO$_2$) hydrogels incorporating magnetic nanoparticles (MNPs) offer a promising platform for advanced materials with applications in biomedicine. This study explores the synthesis, structural characteristics, and magnetic behavior of SiO$_2$ hydrogels functionalized with MNPs, focusing on their tunable properties. The integration of MNPs within the hydrogel matrix enables controllable magnetic responsiveness while preserving the hydrogel’s inherent porosity and mechanical flexibility [1, 2].

The hydrogel matrix provides a biocompatible and porous environment, enhancing nanoparticle stability and facilitating controlled interactions with external stimuli. In biomedicine, these hybrid materials show great potential for targeted drug delivery, controlled release systems, magnetic hyperthermia for cancer therapy, and biosensing applications. Their magnetic properties enable precise localization and external manipulation, making them ideal for non-invasive therapeutic and diagnostic techniques [3].

We investigate the effects of MNPs size and distribution on the hydrogel's rheological and magnetic properties, providing insight into their stability, responsiveness, and potential for remote actuation. Our findings demonstrate that optimized SiO$_2$-MNPs hydrogels exhibit enhanced magnetic control without compromising structural integrity, paving the way for novel smart materials with multifunctional capabilities.

Acknowledgements

This work was supported by the Slovak Research and Development Agency under the contracts APVV-20-0512 and APVV-23-0097. It was also supported by VEGA 1/047/25 and by the EU NextGenerationEU through the Recovery and Resilience Plan for Slovakia under the project No. 09I03-03-V03-00034.

References

[1]V. Ghobadifar et al., “Synthesis and Characterization of MNPs Hydrogel with pH-Responsiveness Properties to Release Diclofenac Sodium as a Model Drug,” Iran. J. Chem. Chem. Eng., vol. 42, no. 3, Mar. 2023, https://doi.org/10.30492/ijcce.2022.545387.5085
[2] I. Morales et al., “Magnetic nanoparticle-based hydrogels as reliable platforms to investigate magnetic interactions,” Nanoscale, vol. 17, no. 10. Royal Society of Chemistry (RSC), pp. 5993–6003, 2025. https://doi.org/10.1039/d4nr04286g
[3] A. Vashist et al., “Recent advances in nanogels for drug delivery and biomedical applications,” Biomaterials Science, vol. 12, no. 23. Royal Society of Chemistry (RSC), pp. 6006–6018, 2024. https://doi.org/10.1039/d4bm00224e

Speaker: Dr Jaroslava Szűcsová (Pavol Jozef Šafárik University in Košice, Faculty of Science, Institute of Physics)

56 Magnetic Nanoparticles With Different Shapes for Magnetic Separation of DNA/RNA

Magnetic core-shell nanoparticles (MNPs) possess specific properties (nanoscale size, disposition of magnetic properties, good biocompatibility) that allow to improve various therapeutic methods or laboratory diagnostic techniques, include the field of separation of biomolecules such as various proteins or DNA/RNA molecules [1]. The specificity of different viral and bacterial diseases limits the possibilities of using conventional separation techniques due to the low concentration of the captured target substances and the requirement for large sample volumes. One promising approach in this field is magnetic separation using MNPs, which can interact and bind target molecules due to their large reaction surface [2]. The magnetic properties of MNPs are able to reduce the time-consuming nature of the whole separation process due to the rapid separation of the target substances from the biological sample using an external magnetic field. The target DNA molecules are separated from the surface of the MNPs in the next step at a significantly higher concentration than in traditional methods and subjected to further analysis [3].

The aim of our work was to design, synthesize and characterize magnetic nanoparticles suitable for magnetic separation. We prepared Fe$_3$O$_4$ MNPs, which are also commonly used in commercial applications, to be able to compare the performance of our MNPs. The MNPs prepared by us are exceptional in their shape, where we prepared samples in cubic and star shapes in addition to spherical ones, due to the increase in the reaction surface. We characterized the MNPs in terms of their structure, morphology, magnetic properties and investigated their separation properties.

Acknowledgements

This work was supported by the Slovak Research and Development Agency under the contracts No. APVV-20-0512 and VEGA 1/0470/25.

References

[1] J. He et al., “Magnetic separation techniques in sample preparation for biological analysis: A review,” Journal of Pharmaceutical and Biomedical Analysis, vol. 101. Elsevier BV, pp. 84–101, Dec. 2014. https://doi.org/10.1016/j.jpba.2014.04.017
[2] X. Hu et al., “Preparation and evaluation of solid-phase microextraction fiber based on molecularly imprinted polymers for trace analysis of tetracyclines in complicated samples,” Journal of Chromatography A, vol. 1188, no. 2. Elsevier BV, pp. 97–107, Apr. 2008. https://doi.org/10.1016/j.chroma.2008.02.062
[3] A. Muhammad et al., “Detection of SARS-CoV-2 using real-time polymerase chain reaction in different clinical specimens: A critical review,” Allergologia et Immunopathologia, vol. 49, no. 1. Codon Publications, pp. 159–164, Jan. 08, 2021. https://doi.org/10.15586/aei.v49i1.60

Speaker: Michael Barutiak (Pavol Jozef Šafárik University in Košice, Faculty of Science, Institute of Physics)

57 Magnetism in GdMn$_{1-x}$Ti$_x$O$_3$ ($0.0 \leq x \leq 0.1$) Multiferroic System

GdMnO$_3$ came to the attention of the scientists due to the discovery of multiferroicity in this compound. It crystallizes in the orthorhombically distorted perovskite structure; space group $Pnma$; Gd ions are located on $4c$; Mn ions on $4b$ and oxygen anions are located on $4c$ and $8d$ crystallographic sites. The compound orders into antiferromagnetic phase below $T_N\sim 40$ K [1] and then undergoes order-to-order magnetic phase transition into low temperature canted magnetic phase at $T_{lock}$ ($\sim 20$ K). The opened question is, if the magnetism and multiferroicity can be tuned in order to increase application potential of this material. In our previous paper we reported on Mn-Fe substitution [2] and our present study is focused on Mn-Ti substitution.

GdMn$_{1-x}$Ti$_x$O$_3$ compounds were synthetized by the floating zone method and structural analysis of final compounds was carried out through Rietveld refinement. It was found that the samples up to $x=0.1$ are single-phase with the crystal structure related to GdMnO$_3$ parent compound. For $x>0.1$, the impurity phases were detected which restricts the study of this system to low Ti concentrations. The Ti substitution shifts the lattice parameters from $a=5.852(2)$ Å; $b=7.423(3)$ Å and $c=5.310(2)$ Å to $a=5.837(1)$ Å; $b=7.484(1)$ Å; $c=5.329(1)$ Å. The Neel temperature $T_N$ is not visible on magnetization measurements, however, from the combination of zero-field-cooled; field-cooled magnetization data and hysteresis loops $M$(B) we concluded the decrease of $T_N$ from $42$ K ($x=0$) to roughly $30$ K ($x=0.1$). $T_{lock}$ has been also shifted from $\sim 20$ K ($x=0$) to $\sim 2$ K ($x=0.1$). In the temperature interval $T_{lock}

In the contribution, we present a comprehensive study of GdMn$_{1-x}$Ti$_x$O$_3$ ($0\leq x\leq0.1$) substitutional system. To ensure a thorough understanding, we compare and discuss our results with results obtained by other groups for the concentrations, for which the data are available.

Acknowledgements

This publication is the result of the project implementation: VEGA 2/0004/25.

References

[1] N. Pavan Kumar et al., “Specific heat and magnetization studies ofRMnO3(R=Sm, Eu, Gd, Tb and Dy) multiferroics,” Physica Scripta, vol. 83, no. 4. IOP Publishing, p. 045701, Mar. 08, 2011. https://doi.org/10.1088/0031-8949/83/04/045701
[2] M. Mihalik Jr. et al., “Magnetism of GdMn1-xFexO3 (0≤x≤1) Nanoparticles,” Acta Physica Polonica A, vol. 137, no. 5. Institute of Physics, Polish Academy of Sciences, pp. 993–996, May 2020. https://doi.org/10.12693/aphyspola.137.993

Speaker: Muhammad Faisal Ashraf (Institute of Experimental Physics, Slovak Academy of Sciences)

58 Magnetization as Probe for Purity of Schwertmannite

Schwertmannite, a poorly crystalline iron oxyhydroxysulfate, is an iron-bearing mineral that plays a pivotal role in various environmental processes, particularly in the treatment of acidic mine drainage [1]. Due to its ability to adsorb metal ions, anions, and its high surface area-to-volume-ratio, Schwertmannite has drawn significant attention as a potential medium for mitigating environmental contamination [2]. However, its poorly crystalline structure presents challenges in characterizing its composition, making it difficult to detect and quantify trace impurities. One such impurity is goethite, another iron mineral that can form under similar conditions due to higher thermodynamical stability [3]. Differentiating between schwertmannite and goethite in environmental samples or synthetic preparations is critical, as the presence of goethite influences the chemical reactivity and stability of schwertmannite, altering its efficiency in ecological applications.

The aim of this study is to explore the use of magnetic measurements obtained from a Vibrating Sample Magnetometer (VSM), to detect goethite impurities in schwertmannite. Goethite typically has a higher magnetization and a different temperature dependence of its magnetic properties compared to schwertmannite. The presence of trace amounts of goethite can, therefore, be detected through careful analysis of the magnetic response of the sample. In this study, Schwertmannite samples with different concentrations of goethite were synthesized with an environmentally friendly and fast method, and the effect of the impurities on the properties of the resulting materials was investigated with VSM, XRD, FT-IR, $^{57}$Fe Mössbauer spectroscopy, and TEM analyses. The VSM allows for the precise measurement of the magnetic moment of the sample as a function of an applied magnetic field, providing detailed insights into the magnetic behavior of the mineral phases present. This sensible and accurate detection was the only technique capable of detecting the presence of goethite even in the purest sample.

These findings demonstrate that VSM-based magnetic characterization can serve as an effective tool for identifying goethite impurities in schwertmannite and contribute to the knowledge about the characterization of poorly crystalline iron materials, and highlight the potential of magnetic techniques for improving our understanding of these materials in natural and engineered systems.

References

[1] J. M. Blgham et al., “A poorly crystallized oxyhydroxysulfate of iron formed by bacterial oxidation of Fe(II) in acid mine waters,” Geochimica et Cosmochimica Acta, vol. 54, no. 10. Elsevier BV, pp. 2743–2758, Oct. 1990. https://doi.org/10.1016/0016-7037(90)90009-a
[2] B. Marouane et al., “The potential of granulated schwertmannite adsorbents to remove oxyanions (SeO32−, SeO42−, MoO42−, PO43−, Sb(OH)6−) from contaminated water,” Journal of Geochemical Exploration, vol. 223. Elsevier BV, p. 106708, Apr. 2021. https://doi.org/10.1016/j.gexplo.2020.106708
[3] P. Acero et al., “The behavior of trace elements during schwertmannite precipitation and subsequent transformation into goethite and jarosite,” Geochimica et Cosmochimica Acta, vol. 70, no. 16. Elsevier BV, pp. 4130–4139, Aug. 2006. https://doi.org/10.1016/j.gca.2006.06.1367

Speaker: Cristian Pilloni (Department of Inorganic Chemistry, Charles University)

59 Measurement of Pressure and Temperature of the Automobile's Brake System using a Contactless Sensor

The design and implementation of a contactless pressure and temperature measurement system for an automotive brake assembly, utilizing glass-coated magnetic microwires, is presented. Amorphous microwires, produced by the Taylor-Ulitovsky method, possess distinctive magnetic characteristics - most notably, magnetic bistability, a pronounced Barkhausen jump, and the influence of pressure on the value of the critical switching field. These properties facilitate the detection of pressure and temperature changes through corresponding shifts in the critical switching field, which are measured by a dedicated pickup coil.

The experimental set-up consists of genuine brake components (including a brake master cylinder, brake booster, brake lines, and a brake caliper with a rotor) rigidly mounted to a support structure. Two coils (an excitation coil and a pickup coil) are employed. The excitation coil generates a triangular AC magnetic field that provokes the microwire’s magnetization reversal, while the pickup coil records the resulting voltage impulses. Pressures of up to 60 bar were applied and monitored, and the brake fluid temperature was altered by an external heating mechanism to assess the microwire’s response to thermal changes.

The measured dependences confirm that glass-coated microwires can reliably track changes within the brake system without the need for direct modification of the hydraulic assembly. This technology thus holds potential for high-accuracy and safe measurement of pressure and temperature in automotive applications, particularly where contactless sensing and robust performance under mechanical stress are essential. In addition, the results outline several areas for further research, such as improving sensor sensitivity and minimizing interference from external magnetic fields in real-world environments.

Speaker: Mr Samuel Onufer (RVmagnetics a.s.)

60 Mesoporous Silica Coated Magnetic Nanoparticles for Targeted Delivery of Antithrombotic Drugs

Magnetic mesoporous silica nanoparticles (MSNs) represent a sophisticated category of nanomaterials combining magnetic responsiveness with the versatile drug delivery capabilities of mesoporous silica. Their distinctive structure, characterized by a mesoporous silica shell encapsulating superparamagnetic iron oxide cores, enables efficient drug loading, controlled therapeutic release, and precise targeting through external magnetic fields [1]. This research specifically explores the synthesis and application of magnetic MSNs for targeted delivery of antithrombotic drugs, providing an innovative approach for treating thrombotic conditions by delivering medications directly to blood clots with improved precision. Particularly, their magnetic guidance could significantly enhance rapid and precise localization of blood clots, allowing reduced drug dosages and minimizing systemic side effects.

The nanoparticles were synthesized by a coprecipitation method, followed by hydrolysis of tetraethyl orthosilicate (TEOS) in a basic environment to form a SiO$_2$ layer surrounding the iron oxide (Fe$_3$O$_4$) magnetic core. Subsequently, an additional porous silica layer was introduced using cetyltrimethylammonium bromide (CTAB) and polyethylene glycol (PEG) surfactants as pore-generating agents. Nanoparticle characterization involved nitrogen adsorption/desorption measurements, thermal analysis, infrared spectroscopy, X-ray diffraction, transmission and scanning electron microscopy (TEM and SEM). Results indicated that nanoparticles synthesized with CTAB and PEG demonstrated optimal properties for drug delivery applications due to their pore size distributions ($3.2–4$ nm and $2–4$ nm, respectively) and high specific surface areas ($480$ m$^2$/g and $320$ m$^2$/g, respectively), significantly enhancing drug encapsulation capacity.

A detailed analysis of the magnetic properties was performed using SQUID magnetometry, including measurements of magnetic hysteresis loops (magnetization curves, $M$(H)) and temperature-dependent magnetization curves in the zero-field-cooled and field-cooled (ZFC/FC) regimes. These studies confirmed the superparamagnetic behaviour and responsiveness to external magnetic fields, highlighting their suitability for precise magnetic targeting applications. The magnetic properties are crucial to achieving selective nanoparticle accumulation at thrombotic sites through external magnetic guidance, as well as optimizing nanoparticle penetration and diffusion into clot tissue by adjusting magnetic field intensity.

Acknowledgements

Funded by the EU NextGenerationEU through the Recovery and Resilience Plan for Slovakia under the project No. 09I03-03-V04-00722.

References

[1] C. Comanescu, “Magnetic Nanoparticles: Current Advances in Nanomedicine, Drug Delivery and MRI,” Chemistry, vol. 4, no. 3. MDPI AG, pp. 872–930, Aug. 27, 2022. https://doi.org/10.3390/chemistry4030063

Speaker: Dr Eva Beňová (Institute of Chemistry, P. J. Šafárik University, Moyzesova 11, 040 01, Košice, Slovakia)

61 MI-sensing Properties of CoSiB Amorphous Wires

Among plenty of examined magnetoimpedance (MI) materials researchers focus on cobalt-based alloys which are very well-known as soft magnetic materials appropriate for sensing elements [1] in cylindrical (wires) or planar (ribbons or thin films) geometries. This paper presents the results of testing the properties of the MI-element of Co$_{72.5}$Si$_{12.5}$B$_{15}$ amorphous wires, with a diameter of about 110 $\mu$m, at the beginning of the intermediate frequency range (1 MHz $\leq f \leq$ 12 MHz), positioned in a longitudinal DC external magnetic field with intensity of $H_{max}$ = 15 kA/m.

The complex MI-modulus $Z(H,f)$ exhibits a constant increase of $Z(H)$ with frequency, as well as the peak behavior observed for all frequencies, indicating the growth of the rotational magnetization contribution appearing above the domain wall relaxation frequency. These MI-profiles peaks are positioned at the anisotropy field $H_{k}$, suggesting the dominance of rotation magnetization in the circular permeability. The attained peak values of the impedance modulus of almost 100 $\Omega$ were registered at the highest frequency of 12 MHz. The $(\Delta Z/Z)_{max}$ value of 384 $\%$ was registered at a frequency of 1 MHz, while with a further increase in frequency, a constant decrease was recorded, resulting from a decrease in circular permeability.

A linear increase of the magnetic anisotropy field $H_{k}$ is observed in the frequency range $f \in$ [1 MHz, 7 MHz], that is very similar to the already observed $H_{k}(f)$ behavior of amorphous CoFeSiB wires [2]). This linear (and almost threefold enlargement) is followed by a further huge increase of $H_{k}$ in the frequency range from 8-12 MHz. The frequency dependence of the MI-ratio with the magnetic field as a parameter exhibits the maximum value of 365$\%$ ($@$ 1 MHz, 99 A/m), confirming the reliable detection of a weak magnetic field.

Acknowledgments

This research is supported in part by the Ministry of Science, Technological Development and Innovation of the Republic of Serbia and these results are parts of Grant No. 451-03-137/2025-03/200132 with the University of Kragujevac - Faculty of Technical Sciences, Čačak.

References

[1] K. Mohri, M. Yamamoto, and T. Uchiyama, “Application Topics of Amorphous Wire CMOS IC Magneto-impedance Micromagnetic Sensors for I-o-T Smart Society,” Journal of Sensors, vol. 2019, Wiley, Article 8285240, Nov. 2019. https://doi.org/10.1155/2019/8285240.
[2] J. M. Orelj, N. S. Mitrović, V. B. Pavlović, “MI-sensor Element Features and Estimation of Penetration depth and Magnetic Permeability by Magnetoresistance and Magnetoreactance of CoFeSiB Amorphous Wires”, IEEE Sensors Journal, vol. 23, no. 13. Institute of Electrical and Electronics Engineers (IEEE), pp.14017-14024, Jul. 2023, https://doi.org/10.1109/jsen.2023.3274598.

Speaker: Prof. Nebojša Mitrovic (Faculty of Technical Sciences Čačak, University of Kragujevac, Serbia)

62 Multiferoic BaErFeO$_4$: Mössbauer Spectroscopy Study

Multiferroic materials with magnetic, ferroelectric and ferroelastic ordering have drawn significant attention because of the fundamental physics as well as their potential applications for future electronic devices. A sample of polycrystalline BaErFeO$_4$ was prepared by conventional solid-state method. It has an orthorhombic crystal structure with $Pnma$ space group and lattice parameters $a=13.11080(3)$ Å, $b=5.68412(1)$ Å, $c=10.22506(2)$ Å [1] at room temperature. Fe$^{3+}$ ions are located in two different crystal environments, FeO$_5$ square pyramids (atom Fe$1$) and FeO$_6$ octahedra (atom Fe$2$).

At room temperature, the Mössbauer spectrum of BaErFeO$_4$ recorded in the velocity range of $\pm4$ mm/s, consists of two doublets D$_1$ and D$_2$ with close values of isomer shift ($IS$) of $0.37$ and $0.30$ mm/s but with markedly different quadrupole splittings ($QS$) of $0.25$ and $0.50$ mm/s, respectively. The first doublet D$_1$ with larger $IS=0.37$ mm/s corresponds to the ferric ions in the octahedral surrounding (Fe$_2$O$_6$) and the second doublet D$_2$ with smaller $IS=0.30$ mm/s can be attributed to the ferric ions in square pyramids (Fe1O$_5$). Furthermore, Mössbauer spectra of BaErFeO$_4$ were collected at low temperatures ranging from $4.2$ to $55$ K. The paramagnetic doublets remain unchanged down to $T_{N_1}\sim 49$ K [1, 2], below which the spectra are split into magnetic sextets, indicating an onset of the magnetic ordering of iron ions. The spectrum at $40$ K was fitted by two sextets with very broad continuous distributions of the hyperfine magnetic field, which indicate an antiferromagnetic ordering of the iron magnetic moments in the form of an incommensurate spin-density wave [2], where the magnitudes of the iron magnetic moments (and thereby of the hyperfine magnetic field) change dramatically. Below the transition temperature $T_{N_2}\sim 34$ K [1, 2] at temperatures $30$ K, $20$ K and $10$ K in zero external magnetic field, the spectral shapes are narrow and well resolved, and they can be decomposed into two well-separated sextets S$_1$ and S$_2$ corresponding to the two nonequivalent Fe sites, which is consistent with a commensurate antiferromagnetic structure below $T_{N_2}$ [2]. At liquid helium temperature ($4.2$ K) in zero external magnetic field, the width of the distribution of the hyperfine magnetic field in the sextet S$_2$ belonging to pyramidal sites increases to the value $\Delta B_{eff}=1.7$ T, compared with the value $\Delta B_{eff}=0.5$ T observed at $10$ K. The broadening of the lines in the sextet is probably caused by a change in the orientation of the magnetic moments in the sublattice by the influence of spontaneous noncollinear ordering of the Er magnetic moments.

Acknowledgements

The support by the project GA ČR 25-16097S is gratefully acknowledged. The authors thank Prof. N. T. Dang for providing the sample.

References

[1]A. A. Belik et al., “Different magnetic and magnetodielectric behavior of BaRFeO4 ferrites with R = Ho, Er, Tm, and Yb,” Journal of Alloys and Compounds, vol. 922. Elsevier BV, p. 166297, Nov. 2022. https://doi.org/10.1016/j.jallcom.2022.166297
[2] A. Dönni et al., "Er-driven incommensurate to commensurate magnetic phase transition of Fe in the spin-chain compound BaErFeO4" Physical Review B, vol. 109, no. 6. American Physical Society (APS), Feb. 02, 2024. https://doi.org/10.1103/physrevb.109.064403

Speaker: Jaroslav Kohout (Charles University, Faculty of Mathematics and Physics)

63 Multifunctional Magnetic Nanomaterials for Biomedical Applications

Most biological processes take place at the nanoscale, allowing us to understand these processes and create new materials due to technical progress. Magnetic nanomaterials have considerable potential for use in medicine, e.g. in the distribution of the drug to the affected areas, in imaging, and therapy.

In this work, magnetite (Fe$_3$O$_4$) nanoparticles were prepared and functionalized with bovine serum albumin (BSA) to enhance their stability and biocompatibility. Reaction conditions (especially pH) significantly affected the binding of BSA and the stability of the complex. The surface modification of the nanoparticles was designed to support the efficient attachment of betulinic acid - a natural triterpenoid with potential anticancer effects.

The characterization of the prepared nanoparticles was carried out using various methods. Hydrodynamic size was measured by dynamic light scattering (DLS), surface charge of the nanoparticles and their stability was studied by electrophoretic mobilities measurements. The iron content and the amount of BSA adsorbed on the nanoparticles surface was evaluated by UV-VIS spectroscopy. The FTIR spectroscopy was applied to identify the functional groups involved in the BSA binding. The size and shape of the magnetic nanoparticle cores was obtained by transmission electron microscopy (TEM), and the magnetic properties of nanoparticles were studied by the vibrating-sample magnetometry (VSM).

The average size of bare nanoparticles obtained using TEM was $8$ nm. The results suggest that the optimized conditions enable efficient functionalization of magnetic nanoparticles, with potential applications in magnetic resonance imaging (MRI) diagnostics and disease treatment.

Acknowledgements

This work was supported by the Slovak Research and Development Agency under the contract no. APVV-DS-FR-22-0037 and Slovak Grant Agency VEGA 02/0049/23.

Speaker: Valentín Jedinák (Institute of Experimental Physics, Slovak Academy of Sciences)

64 N-Acetylcysteine Designed Magnetic Nanoparticles for MRI

The era of Covid-19 reminds us how difficult it is to treat patients with acute respiratory distress syndrome (ARDS) therefore monitoring of the spatial distribution of the directly administrated drug to the lungs is very demanded.

In this work, we focused on the synthesis, functionalization of magnetic nanoparticles, N-acetylcysteine conjugation to magnetic nanoparticles and the study of drug distribution in the lungs in the aforementioned ARDS by magnetic resonance imaging (MRI). N-acetylcysteine (ACC) is a mucolytic drug commonly used in the treatment of the respiratory tract. The drug dissolves all the components that cause mucus to become viscous and thus promotes expectoration. The first step was the preparation of a conjugate consisting of magnetic nanoparticles modified with amino functional groups suitable for drug conjugation. Nanoparticle functionalization and drug conjugation were optimized and studied by different physicochemical methods such as SEM and TEM, Dynamic Light Scattering (DLS), Electrophoretic Light Scattering, UV/VIS spectroscopy, or magnetic measurements to obtain information about morphology, size distribution, surface charge, drug and magnetite concentrations and, last but not least, information about magnetic properties.

We managed to prepare conjugate with the optimal ACC loading concentration of $1.2$ mg/ml which corresponds to ACC/MNPs w/w ratio = $5$. Before the study of drug distribution in the lungs using MRI, unconjugated amino functionalized MNPs were first characterized by MRI relaxometry in order to determine MRI relaxation properties in vitro and simultaneously to reveal the spatial distribution of MNPs in the lungs ex vivo. We found prevailing $T_2$ relaxation with high transverse relaxivity values ($r_2 = 509.14$ $\pm$ $15.27$ mM$^{-1}$s$^{-1}$, $r_2^* = 663.58$ $\pm$ $19.91$ mM$^{-1}$s$^{-1}$), which allowed contrast imaging and spatial distribution determination of MNPs in lungs ex vivo.

Acknowledgements

The work was supported by the Slovak Research and Development Agency under contract APVV-DS-FR-22-0037, and by the Slovak Science Grant Agency VEGA - Project No. 2/0049/23.

Speaker: Dr Martina Koneracka (Institute of Experimental Physics, Slovak Academy of Sciences)

65 Non-Ohmic Behavior in [Ni$_{80}$Fe$_{20}$/HfO$_2$]$_n$ Discontinuous Multilayers

Intensive studies on the magnetic and magneto-transport properties of ferromagnetic metal-insulator granular thin films and discontinuous metal-insulator multilayers have been mainly driven by improved parameters compared to GMR structures. At the same time, the issue of the electrophysical properties of composite materials, which differ significantly from those of bulk metal samples and bulk homogeneous films, also remains relevant.

[Ni$_{80}$Fe$_{20}$($d_{Fe}$)/HfO$_2$(3)]$_{10}$/Sub discontinuous multilayer systems (DMS) were prepared by sequential magnetron sputtering on the sapphire substrate. The base pressure in the vacuum chamber was $1\cdot10^{-7}$ Torr. During sputtering, the chamber was filled with Ar ($99.999 \%$, Messer, flow rate $18$ $\mathrm{cm^3\cdot min^{-1}}$) at a constant pressure of $3$ mTorr. For the formation of HfO$_2$ layers, radio frequency (RF) magnetron sputtering with a power of 100 W and a deposition rate of $1$ $\mathrm{nm\cdot min^{-1}}$ have been used. For the Ni$_{80}$Fe$_{20}$ layer formation, DC magnetron sputtering with a power of $100$ W and a deposition rate of $5$ $\mathrm{nm\cdot min^{-1}}$ have been used. The effective thickness of the insulator layer HfO$_2$ was $3$ nm and remained unchanged. The effective thickness of the ferromagnetic layer Ni$_{80}$Fe$_{20}$ changed within the range from $1$ to $3$ nm. The electrical resistance experiments were carried out using the four-point method. The distances between the electrical contacts were $1.27$ and $3$ mm. The deposited films were annealed at the temperature range from $300$ to $573$ K. After that, the low-temperature resistivity measurements from $300$ K down to $10$ K were performed.

It was demonstrated that the structure of the samples consists of magnetic granules separated by insulator channels. The exponential nature of electrical resistance under heat treatment up to $573$ K is observed for all investigated discontinuous multilayer systems. In general, the behavior of electrical resistance as a function of the temperature is described by the equation:
$$R=R_0 \exp⁡(T_0⁄T)^{\alpha}$$ where $T_0$ depends on the concentration of the ferromagnetic metal; $\alpha$ takes values of $1/2$ in the case of thermally activated hopping [1] or $1/4$ in the case of variable range hopping [2]. Linear fitting to $\ln R$ vs. $T^{−1/4}$ and $\ln R$ vs. $T^{−1/2}$ data points for DMS demonstrated that the variable range hopping better represents experimental results. The influence of ferromagnetic layer thickness on the $T_0$ value was shown.

Acknowledgements

This work was funded by the NATO Program "Science for Peace and Security" (project Nr. G6131).

References

[1] P. Sheng et al., “Hopping Conductivity in Granular Metals,” Physical Review Letters, vol. 31, no. 1. American Physical Society (APS), pp. 44–47, Jul. 02, 1973. https://doi.org/10.1103/physrevlett.31.44
[2] R. Rosenbaum et al., “A useful Mott - Efros - Shklovskii resistivity crossover formulation for three-dimensional films,” Journal of Physics: Condensed Matter, vol. 9, no. 29. IOP Publishing, pp. 6247–6256, Jul. 21, 1997. https://doi.org/10.1088/0953-8984/9/29/010

Speaker: Dr Vladimír Komanický (Pavol Jozef Šafárik University in Košice, Faculty of Science, Institute of Physics)

66 Novel One-Pot Synthesis of Strongly Exchange-Couped FeCo-CoFe$_2$O$_4$ Nanocomposites With Tailored Magnetic Properties

Magnetic hybrid nano-architectures, which combine materials with distinct magnetic properties at the nanoscale, enable the development of advanced materials with novel functionalities arising from interface interactions [1]. In this context, exchange-coupled hard/soft nano-heterostructures, combining ferro(i)magnetic phases with high magnetic anisotropy and high magnetization, have garnered significant interest for applications in energy (e.g., permanent magnets), information storage, and biomedicine. However, synthesizing high-quality heterostructures remains complex due to the challenges in achieving well-defined interfaces and strong magnetic coupling. This work proposes a novel one-pot synthesis strategy, previously used to produce metallic nanoparticles, under milder conditions compared to conventional methods [2, 3], based on the reduction and subsequent oxidation of preordered precursor salts. To demonstrate the feasibility of the approach, the study focuses on a model Fe-Co/CoFe$_2$O$_4$ system, comprising a soft Fe-Co metal core with high saturation magnetization and a hard CoFe$_2$O$_4$ ferrite. Crystalline Co-nitroprusside complexes ($1:1$ and $2:1$ Fe:Co ratios) were reduced at $400$ °C in H$_2$ to form metallic cores, followed by controlled oxidation during the cooling process by varying the temperature ($T_i$) at which oxidation is induced from $400$ °C down to $250$ °C (with steps of $50$° C). The results reveal the formation of nanostructured Fe-Co powders dispersed in a CoFe$_2$O$_4$ matrix, exhibiting strong magnetic coupling, as evidenced by single-phase-like hysteresis loops at room temperature. Both coercivity ($H_c$) and saturation magnetization ($M_s$) vary as a function of $T_i$, with the best performance ($\mu_0H_c \simeq 0.1$ T, $M_s \simeq 140$ Am$^2$ kg$^{-1}$) achieved at $T_i= 350$ °C. These results highlight the potential of this approach for producing strongly exchange-coupled systems.

Acknowledgments

This work is supported by the project “Hybrid ferrite nanocomposites for novel rare-earth free permanent magnets” (P2022RRT4_PE5_PRIN2022PNRR)

References

[1] S. Laureti et al., “The role of chemical and microstructural inhomogeneities on interface magnetism,” Nanotechnology, vol. 32, no. 20. IOP Publishing, p. 205701, Feb. 22, 2021. https://doi.org/10.1088/1361-6528/abe260
[2] G. Varvaro et al., “Facile and fast synthesis of highly ordered L10-FeNi nanoparticles,” Scripta Materialia, vol. 238. Elsevier BV, p. 115754, Jan. 2024. https://doi.org/10.1016/j.scriptamat.2023.115754
[3] G. Varvaro et al., “Synthesis of L10 alloy nanoparticles. Potential and versatility of the pre-ordered Precursor Reduction strategy,” Journal of Alloys and Compounds, vol. 846. Elsevier BV, p. 156156, Dec. 2020. https://doi.org/10.1016/j.jallcom.2020.156156

Speaker: Hammad Husnain (CNR-ISM, nM2-Lab)

67 Oscillations of a Single Domain Wall in Alternating Magnetic Field in Bistable Microwire

The domain structure of amorphous ferromagnetic microwires with positive magnetostriction is formed during production with the Taylor-Ulitovsky method of rapid quenching. The stress distribution results in a large axial domain along the microwire, in which the magnetization takes only two opposite states. There are closure domain structures to minimize magnetostatic energy at the ends of the microwire. The magnetization process occurs by releasing the domain wall (DW) from the closure domain structure, but also by nucleating opposite domains and subsequent movement of the formed DWs, if the external magnetic field is high enough. It has been shown that it is possible to create a single DW in the sample far from the ends, which remains there even after the external magnetic field is turned off.

Recently a new experimental set-up to study the dynamics of a DW moved by an alternating sinusoidal (AC) magnetic field was presented [1] in which the microwire is placed in a system of four coaxial coils. A pair of coils in Helmholtz geometry in parallel or antiparallel combination allows the whole wire to be magnetized axially or a single DW to be created in the place of the local zero field, respectively. If this magnetic field is on, the created DW is in an artificial potential well, and if magnetic field is off the DW is in a local well. The AC magnetic field with angular frequency $\Omega$ generated by the magnetizing coil causes the DW to start oscillating. The voltage induced due to DW oscillation is measured through the pick-up coil. The induced voltage as a function of the angular frequency (from $30$ kHz to $800$ kHz) as well as a function of the amplitude of the alternating field can be measured.

In the present work we study the dynamics of a DW forced to oscillate in a well. Frequency dependences show that the DW in a local well leaves the space inside the pickup coil at relatively low value of amplitudes and frequencies of the applied AC field. The model in which the DW is forced to oscillate in a local parabolic potential well does not describe the observed behavior correctly. The reason may be the large wall axial length to wire diameter ratio [1]. In the case of the artificial potential well, the width of which is larger than the magnetizing coil length, the DW remains inside the magnetizing coil. Along with dynamic measurements, static measurements are also presented, providing information about the local environment in which the domain wall moves.

Acknowledgements

This research was supported by VEGA Grant No. 1/0350/24 from the Scientific Grant Agency of the Ministry for Education of the Slovak Republic.

References

[1] J. Onufer et al., “Dynamics of a single domain wall between axial domains in magnetic microwire,” IEEE Transactions on Magnetics. Institute of Electrical and Electronics Engineers (IEEE), pp. 1–1, 2024. https://doi.org/10.1109/tmag.2024.3481468

Speaker: Dr Jozef Onufer (Department of Physics, Faculty of Electrical Engineering and Informatics, Technical University of Košice)

68 Oxygen-Controlled Magnetic and Magnetocaloric Behavior in NdMnO$_{3+\delta}$

Multiferroic NdMnO$_{3+\delta}$ belongs to the family of RMnO$_3$ (R= rare earth) perovskite and exhibits several fascinating properties, including negative magnetization, magnetocaloric effect (MCE), magnetic anisotropy, and spin reorientation (SR) within the Mn sublattice. Materials with a large MCE are highly desirable for magnetic refrigeration technologies, which provide an energy-efficient and environmentally friendly alternative to conventional gas-compression refrigeration. This study aims to investigate the impact of oxygen content on the MCE, critical behaviour, negative magnetization and magnetic anisotropy of NdMnO$_{3+\delta}$ crystals grown by the vertical optical floating zone technique in air, O$_2$ and Ar atmosphere.

The crystals were characterized by X-ray powder diffraction, electron scanning microscopy and thermogravimetric measurements. The significant increase of magnetization below 80 K is observed in $M$-$T$ curves showing the onset of magnetic ordering and the temperature dependent magnetization starts decreasing below $20$ K. Both magnetic transitions are also evident in the AC susceptibility ($\chi$$_{ac}$) curve, i.e., around $60$ K and $15$ K. A negative magnetization is observed in zero field cooled (ZFC) and field cooled (FC) regimes. As the temperature decreases from $50$ K, a reduction in magnetization is observed due to the long-range ordering of Nd$^{3+}$, influenced by competing exchange-coupled FM and weak FM interactions at the Nd$^{3+}$ site. When the magnetic moment reaches zero around $15$ – $50$ K, a negative magnetization emerges in the ZFC and FC regimes, attributed to the SR of Mn$^{3+}$. The M-H curves at different temperatures (i.e., $2$ - $150$ K) showing the presence of ferromagnetism at low temperatures while at high temperature a paramagnetic phase has appeared. The relationship between magnetic entropy $-\Delta S_{M}$ and temperature is used to study the MCE of NdMnO$_{3+\delta}$. A sharp increase of $-\Delta S_{M}$ absolute value is obtained around the ordering temperature ($10$ - $20$ K) of Nd sublattice, due to the rapid change in magnetization of NdMnO$_{3+\delta}$ as a result of the disruption Mn moments orientation resulting from the increased applied field and Nd sublattice ordering.

Acknowledgements

This publication is the result of the project implementation: VEGA 2/0004/25.

Speaker: Izaz Khan (Institute of Experimental Physics, Slovak Academy of Sciences)

69 Polyvinyl Alcohol-Coated Magnetic Nanoparticles for Biomedical Applications

Magnetic nanoparticles (MNPs) are a popular choice for biomedicine due to their intrinsic magnetic properties. To fully utilize their potential, surface modification is essential to ensure their hydrophilicity, biocompatibility, and stability in a physiological environment.

This study focuses on the preparation and characterization of MNPs modified with polyvinyl alcohol (PVA). The MNPs were synthesized using the coprecipitation method with ferrous and ferric salts in an alkaline medium, followed by their dispersion in two PVA solutions with different molecular weights ($M_w = 30 000$ g/mol and $90 000$ g/mol). The prepared samples, referred to as MNPs, PVA$30$-MF and PVA$90$-MF, were characterized by various techniques including electron microscopy (TEM), dynamic light scattering (DLS), and magnetic measurements (SQUID), to study the morphology, particle size distribution and magnetic properties. TEM images revealed the formation of nearly spherical nanoparticles in all the samples with sizes ranging from $8$ to $11$ nm. Magnetic measurements demonstrated ferromagnetic behavior with saturation magnetization (MS) up to $70$ emu/g for uncoated MNPs. Samples PVA$30$-MF and PVA$90$-MF exhibited superparamagnetic behavior. Field-cooled (FC) and Zero-field-cooled (ZFC) measurements of magnetization at an applied field of $100$ Oe resulted in blocking temperature $T_B=86$ and $122$ K for PVA$30$-MF and PVA$90$-MF samples, respectively. These results clearly indicate the presence of a PVA layer on the surface of all individual MNPs. Next, AC susceptibility measurements were performed to calculate average hydrodynamic particle sizes and the outcomes were in good agreement with the results from DLS.

Finally, the catalytic activity of the prepared samples, simulating the function of natural biological enzymes was investigated. The findings indicate that both samples exhibit high catalytic activity resulting in their potential application in biosensing, detection of tumor cells and other biomedical applications.

Acknowledgements

This work was supported by the Slovak Research and Development Agency under the contract no. APVV-DS-FR-22-0037 and Slovak Grant Agency VEGA 02/0049/23.

References

[1] S. Ghosh and A. Jaiswal, “Peroxidase-Like Activity of Metal Nanoparticles for Biomedical Applications,” Nanobiomaterial Engineering. Springer Singapore, pp. 109–126, 2020. https://doi.org/10.1007/978-981-32-9840-8_6

Speaker: Ms Paula Pillárová (Institute of Experimental Physics, Slovak Academy of Sciences)

70 Radiolabeling of Functionalized Magnetic Nanoparticles for Potential Theranostic Use

Amino modified (proline, tryptophan and poly-L-lysine) magnetic nanoparticles were used to design potential theranostic agents for cancer diagnosis and for combined radionuclide and hyperthermia therapy [1]. Detailed characterization of prepared MNPs was performed using of various techniques, such as dynamic light scattering, electron microscopy, magnetization measurements or thermogravimetric analysis. Measurements in an alternating and non-alternating magnetic field were also conducted. For the first time amino acid-functionalized magnetic nanoparticles were labeled with theranostic radionuclides $^{131}$I and $^{177}$Lu. Radiolabeling with $^{131}$I did not provide agents with sufficient radiochemical purity and stability. On the other hand, direct radiolabeling with $^{177}$Lu at room and elevated temperature provided satisfactory results in case of proline and tryptophan modified MNPs. Poly-L-lysine functionalized MNPs obtained by radiolabeling at $80$ °C reached very high radiochemical purity and high in vitro and in vivo stability. Moreover, SAR value obtained for poly-L-lysine functionalized MNPs shows their high potential for the possible hyperthermia application. Biodistribution of radiolabeled functionalized MNPs was studied in healthy male Wistar rats. The results are encouraging for the future research on discovering the full potential of $^{177}$Lu– PLL-MNPs ($80$ °C) for hyperthermia-based cancer treatment in combination with radioactivity.

Acknowledgements

This work was supported by the Slovak Research and Development Agency under the contract no. APVV-DS-FR-22-0037 and Slovak Grant Agency VEGA 02/0049/23.

References

[1] M. Mirković et al., “Design and preparation of proline, tryptophan and poly-l-lysine functionalized magnetic nanoparticles and their radiolabeling with 131I and 177Lu for potential theranostic use,” International Journal of Pharmaceutics, vol. 628. Elsevier BV, p. 122288, Nov. 2022. https://doi.org/10.1016/j.ijpharm.2022.122288

Speaker: Dr Vlasta Závišová (Institute of Experimental Physics Slovak Academy of Sciences)

71 Shape Anisotropy Effect on the Magnetocaloric Performance of Heusler Ni$_{53}$Fe$_{20}$Ga$_{27}$ Microwire

Magnetic refrigeration is an innovative, eco-friendly cooling technology that offers greater efficiency compared to conventional methods. One of its key advantages is the scalability of magnetocaloric materials for various applications. However, reducing the size of the cooling system naturally diminishes its cooling power, which can be compensated by employing higher magnetic field changes. This approach, unfortunately, leads to increased energy consumption.

In this study, strategies to reduce energy demands are explored, by utilising the shape anisotropy of microwire samples. The fabrication process of microwires inherently induces strong shape anisotropy, resulting in an easy magnetisation axis along the wire’s length and a hard magnetisation axis perpendicular to it.

The magnetocaloric effect in Heusler glass-coated Ni$_{53}$Fe$_{20}$Ga$_{27}$ microwires was investigated using indirect magnetic measurements. The results show that sample rotation has impact on the magnetocaloric effect under high magnetic field changes. However, at lower magnetic field changes, the observed behaviour reveals promising opportunities for practical applications. Specifically, the magnetocaloric effect along the hard axis is negligible compared to the effect when the sample is aligned in parallel with respect to the applied magnetic field. This finding suggests the potential for achieving efficient cooling by rotating the sample within a low static magnetic field produced even by permanent magnets.

Acknowledgements

This work was supported by the projects APVV-16-0079 and VEGA 1/0180/23 and vvgs-2024-3079.

References

[1] Y. Liu et al., “Anisotropic magnetocaloric effect in Fe3−xGeTe2,” Scientific Reports, vol. 9, no. 1. Springer Science and Business Media LLC, Sep. 13, 2019. https://doi.org/10.1038/s41598-019-49654-4
[2] M. Hennel et al., “High efficiency direct magnetocaloric effect in Heusler NiMnGa microwire at low magnetic fields,” Journal of Alloys and Compounds, vol. 960. Elsevier BV, p. 170621, Oct. 2023. https://doi.org/10.1016/j.jallcom.2023.170621

Speaker: Miroslav Hennel (UFV, PF UPJS)

72 Simulation and Optimization of the Preparation Process of Soft Magnetic Materials

Soft magnetic materials are an integral part of modern technology, especially in areas such as energy, electrical engineering, automotive and renewable energy. Their properties, such as low hysteretic losses, low coercivity, high relative permeability and low magnetostriction, are crucial for the efficient operation of devices such as transformers, electric motors and inductors. However, the efficient production of these materials requires a thorough understanding and optimisation of the technological processes involved in their preparation.
This work focuses on the simulation and optimization of technological processes for the preparation of soft magnetic materials in order to improve their magnetic, mechanical and thermal properties. Advanced simulation tools such as ANSYS Workbench have been used in the research to enable detailed modelling of the influence of key process parameters such as temperature, pressure, processing time and material composition. The simulations were complemented by experimental methods that provided real data to validate the numerical models. In this work the properties and preparation of Fe-based compacted soft magnetic materials are analyzed. Particular attention was paid to the processes of mechanical surface treatment of powder particles, coating and pressing, which have a major influence on the final properties of the materials. It is expected that optimization of these processes can significantly reduce energy losses, increase magnetic efficiency and improve the mechanical stability of the materials.

Acknowledgements

This work was funded by Scientific Grant Agency of Ministry of Education of Slovak Republic and Slovak Academy of Science grant numbers VEGA 1/0403/23 and VEGA 1/0016/24.

Speaker: Justín Adamko (Technical University of Košice, Faculty of Manufacturing Technologies)

73 Soft Magnetic Properties of FeCoB/Cu Nanocrystalline Ribbons

Nanocrystalline soft magnetic FeCo-based alloys have gained attention in the last decades and recently also in the development of electric motors due to their excellent magnetic properties thanks to their fine microstructure, being composed of bcc-FeCo nanograins surrounded by metalloid-enriched amorphous matrix. FeCoB alloys with high saturation magnetization, low coercivity, high permeability and low core loss have potential applications also in electromagnetic shielding, microwave absorption, electric power transmission, transformers, magnetic sensors, electromagnetic noise suppression [1]. FeCo-based alloys are often used in applications where their high saturation values provide advantage in reducing weight or volume of the components. For example, a careful design of components with FeCo alloys over standard Fe–Si alloys may result in weight savings of $20$–$25\%$ [2].

In this work, we investigated the effect of addition of $1$ at $\%$ Cu to FeCoB alloys on the resulting magnetic properties and microstructure in as-cast state and after nanocrystallization. Rapidly quenched amorphous ribbons were analyzed by DSC to determine critical temperatures. Copper shifts the first crystallization temperature to the lower temperatures. Temperatures close to and above the first transformation ($450$°C – $500$°C) were chosen for heat treatment. The samples were subjected to examination and confirmation of bcc-FeCo phase formation by XRD and TEM after annealing. Magnetic properties of the FeCoB alloy with $1$ at$\%$ Cu addition showed enhancement in magnetic softness after heat treatment in the vicinity of the first crystallization ($450$°C/$30$ seconds). Tendency of $H_c$ to decrease with increasing temperature of annealing correlates with the crystalline fraction content. The achieved magnetic saturation $J_s = 1.92$T is lower compared to Cu free alloy ($J_s = 1.94$T). The achieved results help to optimize the method of annealing and, when another element such as Cu is added, to provide opportunities for the use of such materials in electrical engineering applications.

Acknowledgements

Support of the projects VEGA 2/0120/25, APVV-23-0281, JRP NOMAGRAD and 09I03-03-V01-00047 (Office of Government of Slovakia) is gratefully acknowledged. The study was performed during the implementation of the project "Research of new materials by the methods of advanced diagnostics", ITMS code 313010U400, supported by Research & Innovation Operational Program funded by the ERDF.

References

[1] Y. Yoshizawa et al., “New Fe-based soft magnetic alloys composed of ultrafine grain structure,” Journal of Applied Physics, vol. 64, no. 10. AIP Publishing, pp. 6044–6046, Nov. 15, 1988. https://doi.org/10.1063/1.342149
[2] R. S. Sundar and S. C. Deevi, “Soft magnetic FeCo alloys: alloy development, processing, and properties,” International Materials Reviews, vol. 50, no. 3. SAGE Publications, pp. 157–192, Jun. 2005. https://doi.org/10.1179/174328005x14339

Speaker: Dr Beata Butvinová (Institute of Physics Slovak Academy of Sciences)

74 Stability and Magnetic Ordering Near the Antiphase Boundary in Ni$_2$MnGa

Ni-Mn-Ga alloy is the most promising candidate as material for magnetic shape memory applications. In addition to austenite, it is also found in variety of martensite phases. Antiphase boundaries (APBs) are planar defects that play a critical role in strengthening Ni-based alloys, and their sensitivity to alloy composition offers a flexible tuning parameter for alloy design.

We combine experimental and theoretical (ab initio) methods to analyze the stability and magnetic ordering near the antiphase boundary (APB) in Ni$_2$MnGa with L$_{21}$ ordering. Ab initio electronic structure calculations based on density functional theory are used to investigate the magnetic ordering in a structure simulating APB's in cubic austenite. We show that the magnetic moments of Mn atoms in ferromagnetic austenite are oriented perpendicular to the APB planes. The total energy calculations indicate that at the antiphase boundary the ferromagnetic ordering changes its orientation in the opposite direction. This sudden change in magnetization highlights the APB's, which are then readily visible by magnetic force microscopy. We find that single APB's, when close together, tend to attract each other and form thicker antiphase boundary complexes. Images are shown and discussed.

Acknowledgements

This work was supported by the Czech Science Foundation project 24-11361S.

Speaker: František Máca (FZU - Institute of Physics of the Czech Academy of Sciences)

75 Switching Field Fluctuations in Head-to-Head and Tail-to-Tail Domain Walls in Amorphous Microwires Under Mechanical Stress

This study investigates the switching field fluctuations [1] of head-to-head and tail-to-tail domain walls in amorphous microwires under mechanical stress. Using $7$ cm long samples and analyzing experimental data from $2000$ magnetization cycles, our methodology yields separate switching field distributions for the two domain wall configurations. The experimental results reveal that the fluctuations differ significantly between the head-to-head and tail-to-tail domain walls, with one configuration exhibiting markedly larger variability. These differences may be attributed to variations in domain wall width and a potential unidirectional effect [2], where broader domain walls are more susceptible to structural defects, resulting in sequential detachment from multiple pinning sites. These findings deepen our understanding of the interplay between mechanical stress and domain wall dynamics, emphasizing the importance of individually characterizing head-to-head and tail-to-tail configurations in magnetization reversal processes.

Acknowledgements

This work was supported by the TUKE Research Grant for Young Researchers for the year, awarded by the Technical University of Košice, the Slovak Research and Development Agency under contract No. APVV-16-0079 and VEGA Grant No. 1/0180/23 and No. 1/0350/24 from the Scientific Grant Agency of the Ministry for Education of the Slovak Republic.

References

[1] R. Varga et al., “Switching-field distribution in amorphous magnetic bistable microwires,” Physical Review B, vol. 70, no. 2. American Physical Society (APS), Jul. 02, 2004. https://doi.org/10.1103/physrevb.70.024402
[2] J. Onufer et al., “Unidirectional effect in domain wall propagation observed in bistable glass-coated microwire,” Journal of Magnetism and Magnetic Materials, vol. 396. Elsevier BV, pp. 313–317, Dec. 2015. https://doi.org/10.1016/j.jmmm.2015.08.055

Speaker: Mr Martin Eliáš (Technical University of Košice, RVmagnetics, a.s.)

76 Tailoring the Matteucci Effect in Amorphous Glass-Coated Microwires by Thermal Annealing

Thin magnetic microwires are characterized by peculiar fast domain wall motion. Recently, it was shown that the combination of the high speed of the domain wall and a very small misalignment of the surface magnetization leads to the remarkable Domain Wall Matteucci Effect (DWME). This effect stems from a very small component of the circular magnetization that gives rise to the electrical voltage induced at the ends of the wire through two different mechanisms: (a) by domain wall depinning and (b) by domain wall motion. While the circular component of the surface magnetization can be effectively tailored by mechanical torsion, it remains an open question how the DWME could be enhanced through proper thermal treatment of the samples.

In this contribution, we tailor the magnetic properties of amorphous glass-coated microwires to enhance the DWME. It is shown that thermal annealing of microwires with and without applied torsion remarkably increases the DWME. While the DWME during domain wall motion is correlated only with the speed of the domain wall, the DWME induced by the depinning process is likely related to the complex closure domain structure.

The Magneto-Optical Kerr Effect (MOKE) is used to investigate the direction of the surface magnetization with high precision. Angular dependences of MOKE hysteresis loops are measured along various planes of incidence and linear polarization of the incident light. Theoretical calculations of the magneto-optical contrast for the transverse configuration of MOKE are used to quantify the small misalignment of the surface magnetization.

Finally, our laser-based MOKE loop-tracer [1] is used to correlate the sharp peaks of DWME with the rapid domain wall acceleration/deceleration process invoked by the interaction between the domain wall and pinning sites. The presence of the pinning sites is confirmed by direct imaging using MOKE microscopy.

Acknowledgements

Funded by the EU NextGenerationEU through the Recovery and Resilience Plan for Slovakia under the project No. 09I03-03-V04-00560.

References

[1] O. Vahovsky et al., “Experimental method for surface domain wall shape studies in thin magnetic cylinders,” Journal of Magnetism and Magnetic Materials, vol. 483. Elsevier BV, pp. 266–271, Aug. 2019. https://doi.org/10.1016/j.jmmm.2019.03.015

Speaker: Dr Kornel Richter (Technical University of Košice, Faculty of Electrical Engineering and Informatics)

77 Temperature-Dependent Enhanced Gyrator-Capacitor SPICE Model for Ferrite-Core Inductors With High Permeability

High-permeability ferrite cores are essential components in various electronic applications, particularly in inductors for power electronics and filtering circuits. Accurate simulation of these components is crucial for reliable design, but traditional SPICE models often struggle to capture the temperature-dependent behavior of ferrites. This work introduces an enhanced gyrator-capacitor model specifically tailored to simulate the thermal effects on high-permeability ferrite core inductors. The model incorporates advanced techniques to represent core losses and hysteresis, with a particular emphasis on how these parameters vary with temperature. By integrating thermal modeling with the magnetic model, this research aims to provide a more accurate SPICE-based solution for predicting inductor performance under varying temperature conditions. The developed model will be validated against experimental data obtained from high-permeability ferrite cores, focusing on the correlation between temperature changes and inductor characteristics. This research contributes to improved simulation accuracy, enabling more reliable design of electronic circuits utilizing ferrite core inductors in thermally challenging environments.

Speaker: Piotr Gazda (Warsaw University of Technology, Institute of Metrology and Biomedical Engineering)

78 The Effect of Chromium of the Temperature Dependence of the Switching Field in Iron-Molybdenum-Boron Stage Nano Crystalline Microwire

Contactless sensors are often preferred in applications where physical manipulation with the sensor is not possible or where direct contact could affect the measurements. Microwires can serve as passive sensors which respond to changes in the environment (e.g., magnetic field, temperature) without the need to physically connect them to the measured object. These microwires can be presented as a passive sensor because they do not require an external power source for detection [1].

Temperature dependence using the change in Curie temperature is a very important aspect in the field of materials and sensors, especially in the case of microwires. The change in Curie temperature can be very useful for temperature sensors because microwires exhibit significant changes in magnetic properties when the temperature is close to the Curie point. This change can be detected using contactless methods, such as hysteresis loops. Microwires treated in this way can be used for very accurate and sensitive temperature measurement [2].

In this paper, we want to show, that we can adjust the temperature dependence of microwire parameters depending on the chromium content. This can significantly contribute to the optimization magnetic (Curie temperature) and mechanical properties of the microwire depending on the temperature. Changing the chromium content involves manipulating the structure and composition of the microwire.

Acknowledgements

This work was partially supported by Slovak Grant Agencies VEGA 1/0350/24 and VEGA1/0180/23

References

[1] V. Zhukova et al., “Switching field fluctuations in a glass-coated Fe-rich amorphous microwire,” Journal of Magnetism and Magnetic Materials, vol. 249, no. 1–2. Elsevier BV, pp. 131–135, Aug. 2002. https://doi.org/10.1016/s0304-8853(02)00520-6
[2] P. Jacko et al., “Advantages of Bistable Microwires in Digital Signal Processing,” Sensors, vol. 24, no. 8. MDPI AG, p. 2423, Apr. 10, 2024. https://doi.org/10.3390/s24082423

Speaker: Peter Duranka (TUKE)

79 The Influence of Ni$^{2+}$ Ion Addition on Thermal and Magnetic Properties of $2$CaO-Al$_2$O$_3$-SiO$_2$ Glasses

Ni$^{2+}$-doped calcium-aluminosilicate glasses with gehlenite ($2$CaO-Al$_2$O$_3$-SiO$_2$) composition were prepared with different content of Ni$^{2+}$ ($0.1$, $1.0$, and $3.0$ mol. $\%$). The glasses were prepared by combining solid-state synthesis and conventional melt quenching. The prepared system was studied using X-ray diffraction analysis, differential thermal analysis, and a SQUID magnetometer.

Depending on the Ni$^{2+}$ content, glasses with different colours (from light brown to dark green) were prepared. X-ray diffraction analysis confirmed the amorphous nature of all prepared systems. In the DTA curves of all samples, one exothermic effect was observed with a maximum in the temperature interval ($960$ °C – $984$ °C), which, based on our previous work [1], can be attributed to the crystallization of the gehlenite. The maximum temperature of the crystallization peak decreased with increasing content of Ni$^{2+}$ in the glasses, indicating an increasing tendency to crystallize, and lower heat resistance of doped glasses. The magnetic properties of glasses changed as the Ni$^{2+}$ concentration increased (Ni$^{2+}$ ion is paramagnetic), indicating the incorporation of Ni$^{2+}$ ions into the glass matrix. Magnetization versus external magnetic field dependence at $300$ K indicated that the addition of Ni$^{2+}$ significantly influenced the magnetic properties of gehlenite glasses. First, with increasing Ni$^{2+}$ content, the influence of the diamagnetic component decreases and conversely increases the proportion of the paramagnetic component. In the second row, at low fields, the narrow hysteresis loop was present, indicating the existence of a ferromagnetic component. At $2$ K, only the paramagnetic component of the magnetization is present; however, the influence of this component increases with increasing Ni$^{2+}$ addition. The obtained results are consistent with those of other authors [2] and will be useful in the shaping and further processing of these glasses for magneto-optical applications.

Acknowledgements

The financial support of this work by the projects VV-MVP-24-0456, VEGA 2/0077/24, VEGA 2/0028/21 and VEGA 2/0104/25 is gratefully acknowledged.

References

[1] M. Majerová et al., “Study of thermal properties and crystallization kinetics of Bi-doped 2CaO-Al2O3-SiO2 glasses,” Journal of Thermal Analysis and Calorimetry, vol. 148, no. 4. Springer Science and Business Media LLC, pp. 1533–1541, Oct. 05, 2022. https://doi.org/10.1007/s10973-022-11614-y
[2] S. V. G. V. A. Prasad et al., “Nickel ion—A structural probe in BaO–Al2O3–P2O5 glass system by means of dielectric, spectroscopic and magnetic studies,” Journal of Physics and Chemistry of Solids, vol. 67, no. 12. Elsevier BV, pp. 2478–2488, Dec. 2006. https://doi.org/10.1016/j.jpcs.2006.07.002

Speaker: Melinda Majerová (Department of Magnetometry, Institute of Measurement Science, Slovak Academy of Sciences, Dúbravská cesta 9, SK-842 19 Bratislava, Slovak Republic)

80 Tuning of Nodal Line States via Chemical Alloying in Co$_2$CrX (X = Ga, Ge) Heusler Compounds for a Large Anomalous Hall Effect

Topological materials have attracted significant interest in condensed matter physics for their unique topological properties leading to potential technological applications. Topological nodal line semimetals, a subclass of topological materials, exhibit symmetry-protected nodal lines, where band crossings occur along closed curves in the three-dimensional Brillouin zone. When the nodal lines are gapped out due to perturbation in the Hamiltonian, a large Berry curvature (BC) arises in the surrounding area of the gapped nodal line, leading to exotic anomalous transport responses. In this paper, we studied the Co$_2$CrX (X=Ga, Ge) Heusler compounds that exhibit mirror symmetry-protected nodal line states below the Fermi level. The BC calculation yields anomalous Hall conductivity (AHC) of about $292$ and $217$ S/cm for Co$_2$CrX (X=Ga, Ge), respectively, at the Fermi level, which increases by up to $400\%$ at the nodal line energy level. We theoretically analyzed that $20\%$ and $60\%$ zinc (Zn) alloying in Co$_2$CrX (X=Ga, Ge) effectively lowers the Fermi level by $50$ meV and $330$ meV, respectively, aligning with the protected crossings. Consequently, we identified Co$_2$CrGe$_{0.4}$Zn$_{0.6}$ and Co$_2$CrGa$_{0.8}$Zn$_{0.2}$ as compositions to achieve the significant AHC of $800$ and $1300$ S/cm, respectively. The explicit AHC calculation for these alloyed compositions is in good agreement with our predictions. Our findings highlight that chemical alloying is an efficient way to enhance AHC in nodal line hosting materials.

Acknowledgements

S.W.D and J.M. are thankful for the support of the QM4ST project funded by Programme Johannes Amos Commenius, call Excellent Research (Project No. CZ.02.01.01/00/22_008/0004572). S.S. thanks the Science and Engineering Research Board of India for financial support through the CRG scheme (Grant No. CRG/2021/003256) and UGC-DAE CSR, Indore, for financial support through the CRS scheme.

Speaker: Sunil Wilfred DSouza (New Technologies Research Centre, University of West Bohemia)

Dinner: DINNER with Music Concert

81 Music Performance by IL DUETTO

It is with great pleasure that the organizing committee of the CSMAG'25 invites you to a special evening of music. Come and unwind, connect with fellow attendees, and immerse yourself in a wonderful performance that will enrich the spirit of our gathering.

The concert will take place on Tuesday, July 8, 2025 at 19:00 as part of an event combined with dinner.

Zuzana Oráčová (violin)

After graduating from the Conservatory in Košice, Zuzana continued her studies at the Academy of Performing Arts in Bratislava. Since 2004, she has been a member of the State Philharmonic Orchestra in Košice, where she works as a violinist in the first violin section

Andy Belej (Piano / Singing)

Andy was a member of the opera orchestra of the Jonáš Záborský Theatre and participated in the musical preparation of the musicals Na skle maľované and Pokrvní bratia. From 2011 to 2013, he was a vocalist in the band I.M.T. Smile.

More information can be found at https://www.ilduetto.sk/

Speakers: Mrs Zuzana Oráčová (IL DUETTO), Mr Andy Belej (IL DUETTO)

Concert anouncement

Wed, July 9

Section S7: Rare-earth and 5f-systems

Convener: Mauro Giovannini

82 Lanthanide Coordination Complexes for Quantum Technologies

In recent years we have shown, that molecular Lanthanide-based coordination complexes hold potential for use as physical supports for the implementation of single- and entangled-qubit quantum gates in Quantum Information Technology devices [1,2]. The coupled electronic qubit-nuclear qudit nature of this system allowed to propose a scheme for intrinsic implementation of efficient quantum error correction schemes [2]. Further, the multifrequency single crystal c.w.- and pulse EPR spectra of Gd(trensal), allowed to establish that vanishing angular orbital momentum results in decoherence suppression [3]. In addition, dipolar-interaction-coupled Yb(III) sites were exploited for the experimental demonstration of entangled-qubit gates [4]. Finally, very recently, we demonstrated the first ever implementation of a quantum simulation on molecular magnetic materials [5].

Recently we probed the fundamental factors that induce decoherence in ensembles of molecular magnetic materials [6]. This was done by pulse Electron Paramagetic Resonance measurements at X-band ($\sim9.6$ GHz) on single crystals of Gd$\\@$Y(trensal) at $0.5$, $10^{-1}$ , $10^{-2}$ and $10^{-3}$ $\%$ doping levels. At the lowest dilution level of $10^{-3}$ $\%$, and under dynamic decoupling conditions, the ratio of $T_m$ versus the time it takes to implement a quantum gate, $T_G$, reaches the order of $10^4$, in the example of a single qubit $\pi$-rotation, which corresponds to a gate fidelity of $99.99$ $\%$.

Acknowledgements

We thank the Novo Nordisk Foundation for research grants NNF20OC0065610 and NNF21OC0068806.

References

[1] K. S. Pedersen et al., “Toward Molecular 4f Single-Ion Magnet Qubits,” Journal of the American Chemical Society, vol. 138, no. 18. American Chemical Society (ACS), pp. 5801–5804, Apr. 27, 2016. https://doi.org/10.1021/jacs.6b02702
[2] R. Hussain et al., “Coherent Manipulation of a Molecular Ln-Based Nuclear Qudit Coupled to an Electron Qubit,” Journal of the American Chemical Society, vol. 140, no. 31. American Chemical Society (ACS), pp. 9814–9818, Jul. 24, 2018. https://doi.org/10.1021/jacs.8b05934
[3] C. D. Buch et al., “Spin–Lattice Relaxation Decoherence Suppression in Vanishing Orbital Angular Momentum Qubits,” Journal of the American Chemical Society, vol. 144, no. 38. American Chemical Society (ACS), pp. 17597–17603, Sep. 15, 2022. https://doi.org/10.1021/jacs.2c07057
[4] B. E. Bode et al., “Dipolar-Coupled Entangled Molecular 4f Qubits,” Journal of the American Chemical Society, vol. 145, no. 5. American Chemical Society (ACS), pp. 2877–2883, Jan. 25, 2023. https://doi.org/10.1021/jacs.2c10902
[5] S. Chicco et al., “Proof-of-Concept Quantum Simulator Based on Molecular Spin Qudits,” Journal of the American Chemical Society, vol. 146, no. 1. American Chemical Society (ACS), pp. 1053–1061, Dec. 26, 2023. https://doi.org/10.1021/jacs.3c12008
[6] S. H. Hansen et al., “Probing decoherence in molecular 4f qubits,” Chemical Science, vol. 15, no. 48. Royal Society of Chemistry (RSC), pp. 20328–20337, 2024. https://doi.org/10.1039/d4sc05304d

Speaker: Stergios Piligkos (Department of Chemistry, University of Copenhagen)

83 Magnetic Anisotropy and Frustration in the Triangular-Lattice Magnet NdMgAl$_{11}$O$_{19}$

Triangular-lattice antiferromagnets (TLAFs) provide a versatile platform for exploring frustrated magnetism, where geometric constraints inhibit conventional long-range order and foster exotic quantum states [1]. In these systems, the interplay between spin–orbit coupling and crystal electric field effects induces markedly different behaviors between Kramers and non-Kramers ions; Kramers ions (e.g., Nd$^{3+}$, Yb$^{3+}$) generally exhibit robust single-ion anisotropy and pronounced quantum fluctuations [1]. Within this context, the ReMgAl$_{11}$O$_{19}$ family has garnered considerable interest as an ideal platform for investigating frustrated magnetism [2-3]. Our work centers on NdMgAl$_{11}$O$_{19}$, a representative of this series. High-quality single crystals were synthesized using the optical floating zone method, and comprehensive measurements including magnetic susceptibility, magnetization, and specific heat were performed down to $45$ mK.

Our findings reveal that Nd$^{3+}$ ions in NdMgAl$_{11}$O$_{19}$ realize a Kramers doublet ground state characterized by strong uniaxial anisotropy along the crystallographic $c$-axis. Curie–Weiss analysis yields small negative temperatures, indicative of weak antiferromagnetic coupling. Moreover, a sharp specific heat anomaly near $81$ mK suggests either partial spin freezing or the emergence of short-range correlations. Under moderate magnetic fields, the low-temperature thermodynamics are well described by a two-level Schottky model arising from the Zeeman splitting of the Nd$^{3+}$ doublet, with the extracted $g$-factor in good agreement with magnetization fits.

These results position NdMgAl$_{11}$O$_{19}$ at the group of TLAF frustrated magnetism and rare-earth single-ion anisotropy, offering insights into the interplay of quantum fluctuations and emergent phenomena in complex magnetic systems.

References

[1] L. Savary and L. Balents, “Quantum spin liquids: a review,” Reports on Progress in Physics, vol. 80, no. 1. IOP Publishing, p. 016502, Nov. 08, 2016. https://doi.org/10.1088/0034-4885/80/1/016502
[2] B. Gao et al., “Spin Excitation Continuum in the Exactly Solvable Triangular-Lattice Spin Liquid CeMgAl11O19,” 2024, arXiv. https://doi.org/10.48550/ARXIV.2408.15957
[3] S. Kumar et al., “Induced quantum magnetism on a triangular lattice of non-Kramers ions in PrMgAl11O19,” 2024, arXiv. https://doi.org/10.48550/ARXIV.2410.07885

Speaker: Sonu Kumar (Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University)

84 Electronic and Magnetic Properties of EuZn$_2$P$_2$ Under Pressure

EuZn$_{2}$P$_{2}$ is a narrow-gap semiconductor (0.11 eV) belonging to the Zintl phase family, characterized by mixed ionic and covalent bonding. Although long-range antiferromagnetic order is established only below $23$ K, strong short-range magnetic correlations significantly reduce electrical resistivity well above the ordering temperature, leading to a giant magnetoresistance effect.

The nature of magnetic interactions in EuZn$_{2}$P$_{2}$ remains under debate. We investigated the pressure dependence of the magnetic ordering temperature using DC magnetization measurements in a miniature diamond anvil cell made from nonmagnetic CuBe alloy. Our magnetization measurements reveal a linear increase in magnetization up to $\sim 4$ GPa, followed by a steeper linear rise up to 10 GPa, the limit of our experiment. Notably, no distinct anomaly in electrical resistivity accompanies magnetic ordering. The Néel temperature ($T_N$) at elevated pressures does not correlate with specific features in $R(T)$. Interestingly, the maximum in $R(T)$, although magnetism-related, appears at temperatures higher than the actual T$_N$ at corresponding pressures. We attribute this deviation from an exponentially increasing resistivity trend to magnetic fluctuations that induce the formation of magnetic polarons.

Hydrostatic pressure strongly enhances both the magnetic ordering temperature and the characteristic temperature of short-range magnetic correlations. As pressure increases, the band gap of EuZn$_{2}$P$_{2}$ gradually closes, and the material exhibits metallic-like behavior above $18$ GPa. The giant magnetoresistance effect remains significant even in this high-pressure metallic state and persists up to room temperature. The results suggest that above $18$ GPa, EuZn$_{2}$P$_{2}$ transitions into a ferromagnetically ordered metallic state.

Acknowledgements

The work has been supported by the Czech Science Foundation under the Grants No. 25-16339S. Experiments were performed in MGML (mgml.eu), which is supported within the program of the Czech Research Infrastructures (Project No. LM2023065).

Speaker: Jiří Kaštil (FZU - Institute of Physics of the Czech Academy of Sciences)

85 Influence of Mesh Granularity on the Accuracy of Modeling the Magnetic Flux Density Attenuation of Aluminum-Steel Cases

Recently, a large number of hard disc drives have been decommissioned due to wear and their replacement with more efficient and reliable solid-state drives. However, before the decommissioning, the data stored on the HDD should be erased. This process is typically carried out through degaussing. However, the aluminium-steel casing of HDDs significantly attenuates magnetic flux density. Additionally, HDD construction varies in terms of steel cover thickness, aluminium chassis, and the number of platters, all of which can impact degaussing performance. To understand this attenuation, the magneto-dynamic process must be modelled using methods such as the finite element method (FEM).

However, the optimal modelling parameters for accurately simulating the attenuation effect remain unclear. The paper presents the results of the analysis of the influence of mesh granularity on the accuracy of modelling the magnetic flux density attenuation [2] of the typical aluminium-steel cases presented in Figure 1. Finally, the paper establishes modelling guidelines to optimise the demagnetisation process and enhance its efficiency.

Acknowledgements

The research was carried out within EUREKA project no EUREKA/AI-REC/13/2022 project co-financed by the National Centre for Research and Development (NCBR) in years 2024-2025.

References

[1] J. Maierhofer and D. J. Rixen, “Computing Forces by ECSW-Hyperreduction in Nonlinear Magnetodynamic FEM Problems,” IEEE Transactions on Magnetics, vol. 60, no. 1. Institute of Electrical and Electronics Engineers (IEEE), pp. 1–13, Jan. 2024. https://doi.org/10.1109/tmag.2023.3332210
[2] D. Kopala, “Improved accuracy of FEM fluxgate models based on adaptive meshing,” PRZEGLĄD ELEKTROTECHNICZNY, vol. 1, no. 10. Wydawnictwo SIGMA-NOT, sp. z.o.o., pp. 145–148, Oct. 03, 2024. https://doi.org/10.15199/48.2024.10.27

Speaker: Anna Ostaszewska-Liżewska (Warsaw University of Technology)

10:30 AM Coffee break

Section S8: Strongly correlated electron systems, superconducting materials - PART 1

Convener: Prof. Karol Flachbart (Institute of Experimental Physics, Slovak Academy of Sciences)

86 An Experimental View on Superconductivity in the Superhydrides

The search for room temperature superconductivity has accelerated dramatically in the last few years, driven largely by theoretical predictions that first indicated alloying dense hydrogen with other elements could produce conventional phonon-mediated superconductivity at very high temperatures and at accessible pressures. More recently, the success of structure search methods have identified specific candidates and pressure-temperature ($P-T$) conditions for synthesis. These theoretical advances have prompted in turn improvements in experimental techniques to test these predictions. As a result, experimental studies of simple binary hydrides under pressure have yielded high critical superconducting transition temperatures ($T_c$), of $260$ K in LaH$_{10}$, close to the commonly accepted threshold for room temperature, $293$ K, at pressures near $180$ GPa.

In this talk, I will discuss our recent efforts on the synthesis and characterization of a Lanthanum-based, higher order superhydride [1]. I will emphasize in particular the experimental methods developed to reach the most extreme conditions required to achieve the synthesis of this new family of superconductors.

Acknowledgements

This work is funded by the Gordon and Betty Moore Foundation through the grant GBMF ID #10731.02

References

[1] A. D. Grockowiak et al., “Hot Hydride Superconductivity Above 550 K,” Frontiers in Electronic Materials, vol. 2. Frontiers Media SA, Mar. 04, 2022. https://doi.org/10.3389/femat.2022.837651

Speaker: Audrey Grockowiak (Leibniz Institute Dresden)

87 Is the Established Theory of Superconductivity Incomplete?

In a series of papers Hirsch argues that the established theory of superconductivity describes neither the dynamics nor the thermodynamics of the Meissner effect in a type-I superconductor, if the magnetic field is switched on before the metal is cooled into the superconducting state. He finds that similar problems appear also when dealing with the process of magnetic field generation in rotating superconductors. His arguments have been summarized in a recent book [1]. Here we examine his criticism in quite detail. To this end, we solve the Maxwell equations supplemented by the simplest established constitutive equation for a superconductor, namely the London equation. We demonstrate that, even at this level of description, the established theory does resolve the problems identified by Hirsch. Surprisingly, the dynamics of the studied processes turns out to be quite rich and interesting.

Acknowledgements

This work was done in collaboration with Peter Markoš and supported by the Slovak Research and Development Agency under Contract No. APVV-23-0515.

References

[1] J. Hirsch, Superconductivity begins with H, World Scientific, New Jersey, 2020.

Speaker: Prof. Richard Hlubina (Comenius University Bratislava)

88 Ising Superconductivity in Bulk $4$H$_a$-NbSe$_2$

Spin-valley locking allowing for in-plane upper critical magnetic fields vastly surpassing Pauli limit was first demonstrated in fully two-dimensional monolayers like of NbSe$_2$ [1] with large spin-orbit coupling and broken inversion symmetry. Surprisingly, this Ising superconductivity can be present in layered bulk materials, too. We have clarified the underlying microscopic mechanism of Ising superconductivity in bulk, based on a reduced interlayer coupling between superconducting layers due to intercalation by insulating layers and restricted inversion symmetry in misfit compounds of (LaSe)$_{1.14}$(NbSe$_2$)$_{m=1,2}$ [2,3]. Here, we show that in some transition metal dichalcogenide polytypes Pauli paramagnetic limit is violated even without intercalation. By the specific heat measurements up to 35 T we show that that in the pristine non-centrosymmetric bulk $4$H$_a$-NbSe$_2$ polytype the in-plane upper critical magnetic field exceeds the Pauli limit three times. Ab initio band structure calculations based on experimentally determined crystal structure confirm the spin-valley locking. The theoretical model provides the microscopic mechanism of the Ising protection based solely on broken inversion symmetry [4]. Moreover, the low temperature specific heat measurements in magnetic field applied at different angles with respect to the basal plane and low temperature scanning tunnelling microscopy and spectroscopy are used to analyse the superconducting order parameter.

Acknowledgements

The following grants are acknowledged: Slovak R&D Agency APVV-23-0624, Slovak Academy of Sciences IMPULZ IM-2021-42, VEGA 2/0073/24 and ERC no 865826.

References

[1] X. Xi et al., “Ising pairing in superconducting NbSe2 atomic layers,” Nature Physics, vol. 12, no. 2. Springer Science and Business Media LLC, pp. 139–143, Nov. 09, 2015. https://doi.org/10.1038/nphys3538
[2] P. Samuely et al., “Extreme in-plane upper critical magnetic fields of heavily doped quasi-two-dimensional transition metal dichalcogenides,” Physical Review B, vol. 104, no. 22. American Physical Society (APS), Dec. 20, 2021. https://doi.org/10.1103/physrevb.104.224507
[3] T. Samuely et al., “Protection of Ising spin-orbit coupling in bulk misfit superconductors,” Physical Review B, vol. 108, no. 22. American Physical Society (APS), Dec. 04, 2023. https://doi.org/10.1103/physrevb.108.l220501
[4] D. Volavka et al., “Ising superconductivity in noncentrosymmetric bulk NbSe2,” 2025, arXiv. https://doi.org/10.48550/ARXIV.2501.08867

Speaker: Prof. Peter Samuely (Centre of Low Temperature Physics, Institute of Experimental Physics, Slovak Academy of Sciences)

89 New Ti-rich Yttrium-Containing Superconducting High-Entropy Alloys With High Upper Critical Field

High Entropy Alloys (HEAs) are solid solutions of five or more elements mixed in non-negligible proportions. Their unique and very promising physical properties have attracted much attention since their discovery in $2004$. HEAs form well-defined, close-packed structures (BCC, FCC, HCP). Due to their structural features, HEAs are known for exceptional mechanical properties, thermal stability, and corrosion resistance. These materials have enormous potential for various applications, especially if their high durability is combined with more sophisticated phenomena, such as magnetic ordering and superconductivity. Superconductivity in HEAs was discovered in $2014$. Superconducting HEAs are the new category of disordered superconductors that exhibit substantial robustness against environmental perturbations, i.e., great stability in high pressures and at extreme temperatures. Such properties make them a perfect candidate for high-field magnets in LHC, ITER, or NMR applications.

We present the first results of the synthesis, structural and physical characterization of two new refractory Ti-rich HEA superconductors with Y-addition: Ti$_{0.50}$(YNbTaHf)$_{0.50}$ and Ti$_{0.50}$(ZrNbYHf)$_{0.50}$, possessing a high upper critical field $H_{c_2}$. The alloys were prepared by the arc melting method. The structure of alloys was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDXS). Superconductivity was investigated via electrical resistivity, AC susceptibility, DC magnetization, and specific heat measurements. Additionally, computational calculations within density-functional theory (DFT) were performed. The effect of yttrium on the microstructure and superconducting properties was examined and compared to our previous work on first Ti-rich HEA superconductors [1]. The results showed that both alloys crystallize in a dual-phase structure, dominated by BCC, with a small fraction of HCP. The determined superconducting transition temperatures $T_c$ for Ti$_{0.50}$(YNbTaHf)$_{0.50}$ and Ti$_{0.50}$(ZrNbYHf)$_{0.50}$ are $7$ K and $5$ K, respectively. The relatively high upper critical field of both alloys ($H_{c_2}>13$ T) makes them a new group of potential candidates for high-field magnet applications.

References

[1] P. Sobota et al., “New type of Ti-rich HEA superconductors with high upper critical field,” Acta Materialia, vol. 285. Elsevier BV, p. 120666, Feb. 2025. https://doi.org/10.1016/j.actamat.2024.120666

Speaker: Mr Bartosz Rusin (Institute of Experimental Physics, University of Wrocław)

90 Perspectives of Iron Pnictide and MgB$_2$ Superconductors Discovered in the Third Millennia

This work describes the basic properties of MgB$_2$ ($2001$) and iron pnictide superconductors ($2008$) discovered in the third millennia. Magnetic and transport $J_c(B)$ and $R(T)$ measurements of superconducting wires made of these two materials have been done at low temperatures and external magnetic fields up to $12$ T [1-3]. While MgB$_2$ wires show promising behaviour for the windings generating low or medium DC external fields and also for AC currents and AC fields, iron pnictide conductors are more suitable for high DC magnetic fields. But, high strain tolerances against the Lorentz forces of iron pnictide wires are needed at high magnetic fields, which requires sufficient mechanical reinforcement of soft Sr-$122$/Ag composite e.g. by stainless steel [4-5]. Magnetization AC losses of these superconductors were measured at temperature between $20$ K and $40$ K, AC field of $70$ mT and frequencies $72$ Hz and $144$ Hz. It was found that AC losses are not affected only by superconducting filaments but also by used metallic sheath materials. In the case of Sr-$122$/Ag wire with pure Ag sheath, high contribution of eddy-current losses was observed [6]. Eddy current losses in MgB$_2$ wires were effectively superseded by low purity Cu and Al sheaths. The obtained limits in engineering current density, stress tolerances and AC losses of these third millennia superconductors are presented, compared and discussed in relation to possible practical applications.

References

[1] B. Brunner et al., “Magnetic investigation of silver sheathed Sr0.6K0.4Fe2As2 superconductor,” Physics Procedia, vol. 75. Elsevier BV, pp. 34–40, 2015. https://doi.org/10.1016/j.phpro.2015.12.006
[2] P. Kováč et al., “Behaviour of filamentary MgB2wires subjected to tensile stress at 4.2 K,” Superconductor Science and Technology, vol. 26, no. 10. IOP Publishing, p. 105028, Sep. 12, 2013. https://doi.org/10.1088/0953-2048/26/10/105028
[3] P. Kováč et al., “Current densities and strain tolerances of filamentary MgB2 wires made by an internal Mg diffusion process,” Superconductor Science and Technology, vol. 32, no. 9. IOP Publishing, p. 095006, Jul. 26, 2019. https://doi.org/10.1088/1361-6668/ab27a2
[4] P. Kováč et al., “Electromechanical properties of iron and silver sheathed Sr0.6K0.4Fe2As2tapes,” Superconductor Science and Technology, vol. 28, no. 3. IOP Publishing, p. 035007, Jan. 28, 2015. https://doi.org/10.1088/0953-2048/28/3/035007
[5] F. Liu et al., “Observation of reversible critical current performance under large compressive strain in Sr0.6K0.4Fe2As2tapes,” Superconductor Science and Technology, vol. 30, no. 7. IOP Publishing, p. 07LT01, May 25, 2017. https://doi.org/10.1088/1361-6668/aa6fc1
[6] J. Kováč et al., “Magnetization AC losses of iron-based Ba-122 superconducting tapes,” Cryogenics, vol. 116. Elsevier BV, p. 103281, Jun. 2021. https://doi.org/10.1016/j.cryogenics.2021.103281

Speaker: Pavol Kováč (Institute of Electrical Engineering, Slovak Academy of Sciences)

91 Local Limit Disorder Characteristics of Superconducting Radio Frequency Cavities

Nowadays superconducting radio frequency (SRF) cavities represent fundamental tools used for (Standard Model) particle acceleration, (beyond Standard Model) particle probing, and long-lifetime photon preservation. We study their Quality factor properties mainly at low temperatures within the Dynes superconductor model [1]. We scrutinize and use the local limit response to the external electromagnetic field. Assuming the same regime at low temperatures, we address details of the high-quality plateaus.

Next, studying the sign of the slope of the resonant frequency shift at critical temperature in the moderately clean regime reveals the role of the pair-breaking and pair-conserving disorder. Next, we compare and also fit our results with the recent experimental data from the N-doped Nb sample presented in Ref. [2]. Our analysis remarkably complies with the experimental findings, especially concerning the dip width. We offer straightforward, homogeneous-disorder-based interpretation within the moderately clean regime.

This work presents (and studies the limits of) the simple effective description of the complex problem corresponding to the electromagnetic response in the superconductors combining homogeneous conventional pairing and two different kinds of disorder scattering.

Acknowledgements

This work has been supported by the Slovak Research and Development Agency under the Contract no. APVV-23-0515, by the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie Grant Agreement No. 945478.

References

[1] A. Lebedeva et al., “Local Limit Disorder Characteristics of Superconducting Radio Frequency Cavities,” 2024, arXiv. https://doi.org/10.48550/ARXIV.2409.04203
[2] M. Zarea et al., “Electromagnetic Response of Disordered Superconducting Cavities,” arXiv, 2023, https://doi.org/10.48550/ARXIV.2307.07905

Speaker: František Herman (Department of Experimental Physics, Comenius University)

12:45 PM Conference Photo

1:00 PM LUNCH

SATELLITE MEETING: Magnetic Materials in the Light of Photons, Neutrons and Free Electron Lasers - PART 1

Convener: Dr Jozef Bednarčík (Pavol Jozef Šafárik University in Košice, Faculty of Science, Institute of Physics)

92 The Role of National Contact Point XFEL and ERI for Slovak Research Community

The aim of this talk is to explaine role of main stakeholders preparing policy of Ministy of Education, Ressearch, Development and Youth of the Slovak Republic during the process of establishing SK Infrastructure Roadmap. One of the planned measures is establishing of the National Contact Point for XFEL and other European Research Infrastructures (hereinafter referred to as the NCP XFEL) at Pavol Jozef Šafárik University in Košice.

NCP XFEL has the ambition to help the Slovak scientific community to successfully bid for proposals on the following infrastructures: European XFEL (X-ray Free Electron Laser) GmbH in Hamburg, ILL (Institute Laue Laugevin) in Grenoble, LHC (Large Hadron Collider) in Cerne, ELI Beamlines (Extreme Light Infrastructure) in Czech Republic, EST (EU Solar Telescope) in the Canary Islands, synchrotron radiation sources (without contractual relationship with SK) such as DESY Hamburg, ESRF Grenoble, Solaris Krakow, Diamond Light Source in UK, Alba Synchrotron Barcelona, Spring 8 in Japan, Argonne National Lab. in the USA.

The second aim of the talk is to intorduce main goals of NCP XFEL in the field of research, education, PR, peparing future users, involving industry partnes etc. Due to financial support of NCP XFEL we were able to organize the satellite meeting "Magnetic Materials in the Light of Photons, Neutrons and FELs", bringing together leading experts to discuss the latest advancements in magnetism research. Distinguished scientists will present tutorial lectures about their studies on diverse magnetic materials and phenomena, utilizing state-of-the-art experimental techniques. The session will highlight the unique insights gained from large-scale facilities such as neutron sources, synchrotrons, and free-electron lasers. These powerful tools enable the exploration of spin dynamics, topological magnetism, and emergent quantum effects with unprecedented precision. Through cutting-edge investigations, we aim to deepen our understanding of magnetic interactions at the atomic and nanoscale levels.

Acknowledgements

Organizing Committee would like to acknowledge to NCP XFEL which was founded as a project with the financial support of Ministry of Education, Research, Development and Youth of the Slovak Republic at Pavol Jozef Šafárik University. We also acknowledge to the Faculty of Science, P.J. Šafárik University in Košice – sit of NCP XFEL. We also acknowledge to all tutorial speakers from Large Scale Facilities for their support and contributions to accomplish goals of the Satellite meeting.

Speaker: Prof. Pavol Sovák (Pavol Jozef Šafárik University in Košice, Faculty of Science, Institute of Physics)

93 The SCS Instrument of the European XFEL: A Versatile Tool for Ultrafast Magnetism

The Spectroscopy and Coherent Scattering (SCS) Instrument of the European X-ray Free Electron Laser (European XFEL) offers a wide range of measurement techniques and sample environments for ultrafast studies in solids and liquids. In this talk I will introduce the instrument and its capabilities with an emphasis on applications in magnetism.

The soft X-ray branch of the European XFEL delivers highly energetic femtosecond X-ray pulses at high repetition rates in the photon energy range from 400 eV to 3 keV. A grating monochromator provides tuning over absorption edges with high energy resolution. The photon energy range covers the L- and M-edges of transition metals and rare earth respectively, allowing ultrafast time resolved studies of all magnetic materials of technical relevance. The femtosecond X-ray pulses are complemented by optical lasers spanning from ultraviolet to mid infrared and terahertz for pump-probe experiments.

The experimental techniques offered at the instrument currently include X-ray absorption spectroscopy (XAS), small angle X-ray scattering (SAXS), X-ray diffraction (XRD) and resonant inelastic X-ray scattering (RIXS). Our implementation of XAS is based on a beam splitting scheme using transmission zone plates and an area detector to reach the shot noise limit [1]. With the newly installed elliptical undulators, XAS has been extended to include X-ray magnetic circular dichroism. Magnetic SAXS and coherent diffractive imaging (CDI) can be performed on thin film samples in a transmission geometry using a dedicated end station equipped with fast sample scanning and an out-of-plane electromagnet. Single pulse scattering data can be collected on the DSSC detector at up to 4.5 MHz [2]. The Heisenberg RIXS spectrometer is optimized for solid and liquid jet samples [3]. An end station for solid samples offers X-ray diffraction studies from e.g. spin- or charge ordered systems in combination with RIXS with continuous angle tuning. A liquid jet end station can be coupled to the RIXS spectrometer at fixed angles.

References

[1] L. Le Guyader et al., “Photon-shot-noise-limited transient absorption soft X-ray spectroscopy at the European XFEL,” Journal of Synchrotron Radiation, vol. 30, no. 2. International Union of Crystallography (IUCr), pp. 284–300, Feb. 20, 2023. https://doi.org/10.1107/s1600577523000619.
[2] N. Zhou Hagström et al., “Megahertz-rate ultrafast X-ray scattering and holographic imaging at the European XFEL,” Journal of Synchrotron Radiation, vol. 29, no. 6. International Union of Crystallography (IUCr), pp. 1454–1464, Sep. 29, 2022. https://doi.org/10.1107/s1600577522008414.
[3] J. Schlappa et al., “The Heisenberg-RIXS instrument at the European XFEL,” Journal of Synchrotron Radiation, vol. 32, no. 1. International Union of Crystallography (IUCr), pp. 29–45, Jan. 01, 2025. https://doi.org/10.1107/s1600577524010890.

Speaker: Dr Robert Carley (European X-ray Free Electron Laser Facility GmbH)

94 Imaging the Spin Structure in Self-Assembled Magneto-Resistive Multilayer Nanowires

In this contribution we introduce a novel approach for fabrication of magneto-resistive multilayer nanowires and present their spin structure determination using synchrotron radiation.

Complex nano-structuring routines on magnetic multilayers are frequently applied in data storage and sensor technology to functionalize devices via shape anisotropy. Here we test, if sputter deposition onto nano-facetted surfaces can be applied to form self-assembled, high-quality nanowires with adjustable size and extreme shape anisotropy. Fe/Cr superlattices with intended antiferromagnetic order were deposited in sequences of defined oblique orientation onto a nano-facetted Al$_2$O$_3$ wafer in which the facet morphology was adjusted via high-T annealing [1]. Due to a shadowing effect, well separated magneto-resistive nanowires are formed. A precise nanoscopic characterization, however, is challenging with lab-based techniques. To investigate the structural quality and magnetic properties of the wires we perform conventional as well as nuclear resonant grazing incidence small angle x-ray scattering [2]. While conventional GISAXS is used to extract the relevant parameters of the multilayer morphology, nuclear GISAXS at the $14.41$keV resonance of iron is applied to determine the field-dependent spin structure in the nanowires. These elegant ways for flexible multilayer nanowire formation and novel characterization are highly interesting for potential sensor and device applications requiring tunable magnetic anisotropies.

In this lecture we also discuss experimental conditions, advantages and challenges for similar experiments at a free electron laser.

References

[1] D. J. Erb et al., “Real-Time Observation of Temperature-Induced Surface Nanofaceting in M-Plane α-Al2O3,” ACS Applied Materials & Interfaces, vol. 14, no. 27. American Chemical Society (ACS), pp. 31373–31384, Jun. 28, 2022. https://doi.org/10.1021/acsami.1c22029
[2] D. Erb et al., “Disentangling magnetic order on nanostructured surfaces,” Physical Review Materials, vol. 1, no. 2. American Physical Society (APS), Jul. 17, 2017. https://doi.org/10.1103/physrevmaterials.1.023001

Speaker: Dr Kai Schlage (DESY)

95 Unconventional Altermagnetic Photoresponse by Polarized Light

At a fundamental level, the altermagnetic phase manifests as collinear magnetism characterized by zero net magnetization, highlighting a distinct spin symmetry that emerges from the decoupling of spin and crystal space symmetries. MnTe exemplifies such a material, and Spin- and Angle-Resolved Photoemision Spectroscopy (SARPES) has proven to be an effective method for investigating its altermagnetic electronic structure. Recent findings of spin polarized band structures, coupled with a zero net magnetization in this extensively studied semiconductor, have validated the presence of this unique magnetic order [1]. Further comprehensive ARPES investigations suggest that MnTe-and potentially other collinear altermagnets as well-exhibit an unconventional photoresponse to polarized light that cannot be accounted for by traditional photoemission selection rules. We demonstrate that this phenomenon pertains to both surface-derived bands observed in UV-ARPES and bulk MnTe bands detected in the soft-X regime.

References

[1] J. Krempaský et al., “Altermagnetic lifting of Kramers spin degeneracy,” Nature, vol. 626, no. 7999. Springer Science and Business Media LLC, pp. 517–522, Feb. 14, 2024. https://doi.org/10.1038/s41586-023-06907-7.

Speaker: Juraj Krempaský (Paul Scherrer Institute, Swiss Light Source)

4:00 PM Coffee break

SATELLITE MEETING: Magnetic Materials in the Light of Photons, Neutrons and Free Electron Lasers - PART 2

Convener: Juraj Krempaský (Paul Scherrer Institute, Swiss Light Source)

96 Switching Topological Spin Textures with Photocurrents

The interplay between spin-orbit interaction (SOI) and magnetic order is currently one of the most active research fields in condensed matter physics. Famous examples of this interplay are skyrmions and spin waves, but also the unique properties of altermagnets, the search for Majorana zero modes, and magnetic topological insulators fit directly in this field and have gained much attention in recent years. The full spectrum of possibilities is unleashed in combination with breaking the symmetry of the system, either at interfaces or in the crystal structure itself. This makes multiferroic materials, where symmetry breaking in the form of ferroelectric order and magnetic order coexist, a promising playground to look for functional properties combining SOI and magnetism. Here we will show that starting from a ferroelectric system with strong spin orbit interaction and doping this with magnetic impurities is ndeed a promising pathway to achieve magnetic order with tuneable dynamics. The switching mechanism in this correlated spin glass system will be explained based on stochastic resonance. Furthermore, it will be shown how photocurrents can be used to control the topological spin textures.

In $\alpha$-GeTe the combination of the ferroelectric order and large SOI yields a switchable Rashba-type spin structure of the bulk states. When doped with up to 20$\%$ Mn a magnetic order is induced while the ferroelectric order remains present, rendering it a multiferroic material. Moreover, the strong magnetoelectric coupling in the system ensures a coupling of the magnetisation and polarisation axes, resulting in the opening of a Zeeman gap in the Rashba split bands around the Brillouin zone centre. This unique combination of properties creates a large bulk Rashba-Edelstein effect and allows for current driven magnetisation switching. Here we will present X-ray magnetic circular dichroism (XMCD) and muon spin resonance (muSR) results supported by theory showing that the system orders in a correlated spin glass state with topological spin textures and spontaneously switches its magnetisation direction without changing any of the typical external parameters.

Speaker: Hugo Dil (EPFL Switzerland)

97 Research on the Beamline for Advanced Dichroism Experiments

The beamline for advanced dichroism experiments (BLADE) is a soft x-ray beamline at the UK synchrotron facility Diamond light source. It delivers soft x-ray beam in the energy range from $0.4$ to $1.6$ keV. This energy range is optimized for the dipolar transitions of 3$d$ transition metals ($L_2,_3$ edges) and rare earth elements ($M_4,_5$ edges). So the absorption effect benefits from a strong resonance and directly probes the electronic states responsible for magnetism.

The dichroic effect is measured as difference between circular polarization with opposite handiness in absorption. The absorption is detected by measuring the total electron yield (drain current) and fluorescence signal (photodiode facing the sample) simultaneously.

The absorption branch of BLADE is equipped with superconducting split pair coil that can deliver the magnetic field up to $14$T. The sample can be cooled by a variable temperature insert down to $3$K. The set up is complemented with an electromagnet providing the magnetic field up to $1.5$T. This end station is using a Janis cryostat with the base temperature of $20$K.

In three examples, we demonstrate the capabilities of XMCD and how it can be applied to different magnetic systems. As x-ray magnetic circular dichroism (XMCD) is a resonant effect, the technique is element selective. We recorded the element specific hysteresis loops in exchange biased IrMn/CoFeB interface. The results reveal that Fe spins align antiparallelly with interfacial uncompensated Mn spins, whose strength increases with the decrease in temperature. The uncompensated Mn spins are composed of rotatable and pinned spins. Furthermore, the pinned spins can be switched by annealing under different fields.

Spinel ferrites nanoparticles show significant difference in the surface structure compared to the bulk. This modification also manifests in the redistribution of Fe cations in tetrahedral and octahedral sites. XMCD in combination with the semi-empirical quantum many-body program QUANTY has been used to determine the degree of inversion.

Series of transition metal dopants in single-crystal linearly coordinated molecules are studied by angular dependent XAS and XMCD measurements. $L_2,_3$ edge XAS is developed to be a probe of $3d$–$4s$ mixing via the quantification of ligand-field splitting. Analysis of XAS with support from ab-initio calculations determines the presence of significant $3d$–$4s$ mixing across the transition metal series with maximal mixing for Cu and Ni that then decreases along the series to Mn. XMCD is applied to decompose spin and orbital contributions to easy-plane (Mn and Co) versus easy-axis (Fe and Ni) magnetic behavior.

On the scattering branch of BLADE, soft x-ray diffractometer RASOR (Reflectivity and Advanced Scattering from Ordered Regimes) is equipped with a polarization analyzer, small magnetic field and sample cryostat. It can be used to study the structure and dynamics of the topological objects such as skyrmions.

Speaker: Peter Bencok (Diamond Light Source)

98 Advanced Synchrotron Techniques for Real-Time Analysis of Magnetic and Structural Properties

The I12-JEEP beamline as a part of the national UK synchrotron facility Diamond Light Source (DLS) represents a versatile instrument combining high-energy ($53 – 150$ keV) X-ray scattering and imaging techniques used in the structural characterization of metallic and non-metallic materials, chemical products, geological, biological, archaeological, and palaeontological samples [1, 2]. The extremely high intensity of synchrotron radiation compared to laboratory X-ray sources allows the realisation of in-situ and operando measurements and observations of processes easily with sub-second and millisecond resolution.

Several study examples would be present to envisage that magnetic properties and magnetic interactions can be examined and interpreted indirectly through tools of synchrotron-based X-ray diffraction/total scattering and fast X-ray imaging.

For example, the anomalous thermal expansion known as the Invar effect observed in ferromagnetic Fe-based metallic represents a challenge in our understanding of its manifestation at the atomic scale. It is generally accepted that a high-energy X-ray diffraction (HEXRD) is a critical and indispensable technique to characterise a short-range ordering in metallic glasses and offer an opportunity to link macroscopic material features with atomic structure at the atomic level [3]. In situ HEXRD was able to elucidate the Invar effect in Fe-based metallic glasses at the atomic scale. It was proved that the macroscopic effect has a clear atomistic equivalent in the average Fe-Fe pair distance [4]. Another example underlines the cruciality of better understanding of microstructure formation during casting to welding processes which can be modified by applying an external magnetic field. To follow the formation of precipitates and influence of the magnetic field, high speed synchrotron X-ray imaging/tomography shall be employed [5, 6].

References

[1] M. Drakopoulos et al., “I12: the Joint Engineering, Environment and Processing (JEEP) beamline at Diamond Light Source,” Journal of Synchrotron Radiation, vol. 22, no. 3. International Union of Crystallography (IUCr), pp. 828–838, Apr. 08, 2015. https://doi.org/10.1107/s1600577515003513
[2] https://www.diamond.ac.uk/Instruments/Imaging-and-Microscopy/I12.html
[3] C. J. Benmore, “A Review of High-Energy X-Ray Diffraction from Glasses and Liquids,” ISRN Materials Science, vol. 2012. Hindawi Limited, pp. 1–19, Nov. 14, 2012. https://doi.org/10.5402/2012/852905
[4] A. Firlus et al., “Atomic structure evolution related to the Invar effect in Fe-based bulk metallic glasses,” Nature Communications, vol. 13, no. 1. Springer Science and Business Media LLC, Feb. 28, 2022. https://doi.org/10.1038/s41467-022-28650-9
[5] Z. Song et al., “Revealing growth mechanisms of faceted Al2Cu intermetallic compounds via high-speed Synchrotron X-ray tomography,” Acta Materialia, vol. 231. Elsevier BV, p. 117903, Jun. 2022. https://doi.org/10.1016/j.actamat.2022.117903
[6] J. Wang et al., “Refinement and growth enhancement of Al2Cu phase during magnetic field assisting directional solidification of hypereutectic Al-Cu alloy,” Scientific Reports, vol. 6, no. 1. Springer Science and Business Media LLC, Apr. 19, 2016. https://doi.org/10.1038/srep24585

Speaker: Stefan Michalik (Diamond Light Source Ltd.)

99 Pump-Probe Neutron Inelastic Scattering Experiments

The neutron and, more recently, X-ray spectroscopy have been standard workhorses for investigations of condensed matter dynamics at atomic resolution. Nevertheless, the inherently weak interaction of both probes with matter, accompanied by the tiny flux densities of neutron beams and by the huge Xray photon energy as compared to the energy scale of elementary excitations in condensed matter, have limited their implementation to simple scattering, leaving no options for analogies to optical experiments with coherently split beams.

Experiments using synchronized pulsed Xray and laser beams to investigate the time evolution of non-equilibrium states of condensed matter, both in the structural and in the magnetic domains, are quickly becoming routine at XFEL (X-ray Free Electron Lasers) beams exhibiting picosecond time-structures, accompanied by extreme transversal coherence (e.g. [1]). With neutrons the progress is slower, but reports on successful attempts of time-resolved work have appeared recently as well [2,3] and, after all, a dedicated pump-probe setup has been developed and tested at the SNS Hyspec spectrometer at the ORNL [4].

In this presentation we shall recall the basic principles of scattering theory based on time-dependent correlation functions and review the present state of neutron experimental techniques addressing transient processes in matter, their principal limitations and development opportunities.

References

[1] Y. Lee et al., “A comparative review of time-resolved x-ray and electron scattering to probe structural dynamics,” Structural Dynamics, vol. 11, no. 3. AIP Publishing, May 01, 2024. https://doi.org/10.1063/4.0000249
[2] M. Wang et al., “Optically Induced Static Magnetization in Metal Halide Perovskite for Spin‐Related Optoelectronics,” Advanced Science, vol. 8, no. 11. Wiley, May 02, 2021. https://doi.org/10.1002/advs.202004488
[3] Y. Wang et al., “Monopolar and dipolar relaxation in spin ice Ho 2 Ti 2 O 7,” Science Advances, vol. 7, no. 25. American Association for the Advancement of Science (AAAS), Jun. 18, 2021. https://doi.org/10.1126/sciadv.abg0908
[4] C. Hua et al., “Implementation of a laser–neutron pump–probe capability for inelastic neutron scattering,” Review of Scientific Instruments, vol. 95, no. 3. AIP Publishing, Mar. 01, 2024. https://doi.org/10.1063/5.0181310

Speaker: Jiri Kulda (ILL Grenoble)

100 Panel Discussion - Satellite Meeting

A dynamic panel discussion will be hosted as part of the satellite meeting, Magnetic Materials in the Light of Photons, Neutrons, and FELs. Cutting-edge advances in magnetism research will be explored by leading experts, and groundbreaking studies alongside the transformative role of large-scale facilities, such as neutron sources, synchrotrons, and free-electron lasers, will be highlighted. Trailblazing ideas shaping the future of magnetic materials and phenomena will be engaged with during this event.

Speaker: Juraj Krempaský (Paul Scherrer Institute, Swiss Light Source)

Dinner: Dinner with Miki Knižka

101 Mountain guide Miki Knižka will share his experience with us

Miki Knižka, mountian guide IFMGA / UIAGM

Founder of Mountain Pro Guiding. Adventurer, skier, alpinist… over 10 years of exploring in Canada, ascents to many peaks of South and North America, and various ski touring adventures around the world and in our High Tatras.

The Beginnings - Mountain Sherpa

He was born and grew up under the High Tatras, so he has always been very close to the mountains. Since childhood, He has wandered along the trails in the Tatras, where in addition to the beautiful nature, the mountain sherpas (porters) have won my admiration. He longed to become one of them. His dream came true when he was 17, when his first delivery was to Téry’s Hut. Being a sherpa was everything to him. He pushed the limits of his physical abilities while enjoying the beautiful views of the majestic peaks of the High Tatras. After a while, it wasn’t enough for him to enjoy the views only from the trails, so he wanted to climb the peaks. This is how He gradually got into climbing and ski mountaineering, which He completely fell in love with and found his life’s path in.

Learning about the world and himself

In 1997, he traveled the world for the first time – he spent some time in the USA, earned some money and managed a trip to Alaska. After returning home, he realized that traveling was exactly what he was looking for in life.
Two years later, he found himself in the majestic environment of the Canadian mountains. In Canada, he learned about the possibility of moving to this beautiful country, which was a great challenge for him and it gave him a great desire for adventure.
After returning to Slovakia, together with his friend Juro, they started arranging emigration visas… Unfortunately, Juro never lived to realize this, he was buried in an avalanche in our Tatras.
It was a huge blow for him and it took him almost a year before he finally decided to travel alone to fulfill theirs shared dream.

Achievements he values

The best thing is that he manage to fulfill his dreams in his personal and family life.
Those in the mountains are the icing on the cake:
• 5 x Sherpa Rally winner
• Multiple podium finishes in ski mountaineering races in North America
• Mount McKinley (Denali) – Messner Couloir and West Buttress
• Multi-day ski mountaineering traverses in Canada – Pemberton Icecap traverse, Misty Icefield traverse, McBride traverse, Bugaboos traverse, Bostock-Revelstoke traverse
• During the expedition in South America: climbing the peaks of Artesonraju, Chopicalqui, Huayna Potosi, Parinacota, Quitaraju, Ranrapalca, Sajama, Tocllaraju, Ishinca, Vallunaraju, Pequeno Alpamayo

Speaker: Miki Knižka (Zbojnícka Chata)

Thu, July 10

Section S3: Magnetic materials for energy applications

Convener: Tadeusz Szumiata (Department of Physics, Faculty of Mechanical Engineering, Casimir Pulaski Radom University)

102 Soft Magnetic Materials: Key Technologies Driving Energy Applications

Soft magnetic materials play a crucial role in modern energy applications, enabling higher efficiency, reduced energy losses, and improved performance in electrical devices. Discussion about their fundamental properties, material advancements, and technological innovations, emphasizing their importance in motors, transformers, chokes, and other energy-related applications will be made.

A short overview of soft magnetic materials, including iron-based alloys, amorphous and nanocrystalline materials, and ferrites will be given. Their key properties—such as high permeability, low coercivity, and minimal core losses—will be examined in relation to their impact on electromagnetic performance. Special emphasis will be placed on the significance of saturation induction and material losses in designing optimized materials for specific applications.

A critical focus will be on the role of soft magnetic materials in electric motor applications, where high efficiency is paramount. The growing demand for improved power density and reduced losses in motors used for industrial automation, transportation, and renewable energy systems has driven significant advancements in material processing and optimization. Emerging trends, such as the use of high-silicon steels and cobalt-iron alloys, which enhance motor performance under demanding conditions, will be highlighted.

Advancements in soft magnetic materials also profoundly impact the transformer and inductor markets. Discuss how nanocrystalline and amorphous materials contribute to minimizing core losses, improving efficiency, and enabling compact designs in power conversion systems will be made. Their role in high-frequency applications, including switched-mode power supplies and the grid integration of renewable energy sources, will be analyzed, focusing on their ability to provide low losses and high-frequency stability.

Additionally, innovations in chokes and electromagnetic interference (EMI) suppression components will be addressed. The increasing complexity of power electronics and the widespread adoption of wide-bandgap semiconductors such as SiC and GaN necessitate materials with superior high-frequency characteristics. Advancements in ferrites and composite soft magnetic materials that help overcome these challenges will be examined.

The final section of the presentation will explore future directions and challenges in soft magnetic materials research. Topics such as additive manufacturing, advanced processing techniques, and AI-driven material discovery will be introduced. The potential of machine learning and computational modeling to accelerate material optimization and predict performance under diverse operating conditions will also be discussed.

This comprehensive analysis of soft magnetic materials and their role in energy applications will highlight the latest breakthroughs and inspire further research and development in this critical field.

Speaker: Przemysław Zackiewicz (Łukasiewicz Research Network – Institute of Non-ferrous Metals)

103 Soft Magnetic Materials for Sensor Applications

Wide variety of soft magnetic materials find application as functional materials in magnetic sensors. The requirements for their properties vary, but low coercivity is always expected. Some sensors require high permeability, the others high linearity. Both alloys with small and large magnetostriction, and small and large saturation flux density are required. We will show several sensors developed in our laboratory which are based on improved magnetic materials.

-Commercially available integrated fluxgate sensors have cores made of sputtered permalloy. Using low-magnetostriction amorphous material with induced anisotropy may lower the sensor noise and improve its temperature stability [1].
-Novel nanocrystalline sandwich flake material VITROLAM by Vacuumschmelze has linear loop and large resistance to in-plane eddy currents. It was developed for contactless chargers, but it already has its first sensors application [2].
-Inkjet printing and $3$D printing are attractive methods for the deposition of sensor cores, but the permeability is limited [3].
-Nanocrystalline tapes with flat loop are preferred materials for current transformers. These transformers are resistant not only to DC currents, but also to external DC fields [4].
-New simulation models allow to design structures from arrays of millions of nanowires [5].
-Low-permeability linear magnetic core can increase the sensitivity of Rogowski coil by one order while keeping their excellent linearity [6].
-Microwires from improved CoFeSiB composition were developed for precise orthogonal fluxgate sensors. These sensors achieved noise level well below $1$ $\mathrm{pT/\sqrt{Hz}}$ at $1$ Hz, if the excellent temperature offset stability is not required [7].

Acknowledgements

This work was supported by GACR project 24-12705S Novel Magnetic Position Sensors.

References

[1] J J. Maier et al., “CMOS-based micro-fluxgate with racetrack core and solenoid coils,” Sensors and Actuators A: Physical, vol. 379. Elsevier BV, p. 115886, Dec. 2024. https://doi.org/10.1016/j.sna.2024.115886
[2] P. Ripka et al., “Flat Magnetic X–Y Alignment Sensor,” IEEE Sensors Letters, vol. 8, no. 7. Institute of Electrical and Electronics Engineers (IEEE), pp. 1–4, Jul. 2024. https://doi.org/10.1109/lsens.2024.3414375
[3] D. Hrakova et al., “Inkjet-printed Mn-Zn ferrite nanoparticle core for fluxgate,” Journal of Magnetism and Magnetic Materials, vol. 563. Elsevier BV, p. 170003, Dec. 2022. https://doi.org/10.1016/j.jmmm.2022.170003
[4] P. Ripka et al., “Effect of external DC field on current transformers with amorphous and nanocrystalline cores,” Journal of Magnetism and Magnetic Materials, vol. 563. Elsevier BV, p. 170019, Dec. 2022. https://doi.org/10.1016/j.jmmm.2022.170019
[5] P. Ripka et al., “Apparent permeability of ordered magnetically soft nanowire arrays,” AIP Advances, vol. 12, no. 3. AIP Publishing, Mar. 01, 2022. https://doi.org/10.1063/9.0000316
[6] V. Grim and P. Ripka, “Rogowski Coil With Ferromagnetic Powder Core,” IEEE Magnetics Letters, vol. 13. Institute of Electrical and Electronics Engineers (IEEE), pp. 1–4, 2022. https://doi.org/10.1109/lmag.2022.3143470
[7] M. Butta et al., “An Improved Composition of CoFeSiB Alloy for Orthogonal Fluxgates,” Sensors, vol. 22, no. 6. MDPI AG, p. 2162, Mar. 10, 2022. https://doi.org/10.3390/s22062162

Speaker: Prof. Pavel Ripka (Czech Technical University, Faculty of Electrical Engineering)

104 Origin of MAE and Second Order Anisotropy due to the Magnetostriction in Tetragonal Systems – Example of FePt

The origin of magnetocrystalline anisotropic energy (MAE) guided by spin-orbit coupling in the L1$_0$-FePt alloy was analyzed and the correlations among MAE and magnetoelastic (magnetostriction) constants $b^{\prime}𝑠$($\lambda^{\prime}𝑠$) by means of the electronic structure eigenvalues (orbital energies) and eigenfunctions (orbital occupancies) were established [1]. Our numerical analysis includes the convolution of the projected wave-function (density of states) of each orbital of the Fe and Pt sub-lattices into their orbital energies and its contribution to the MAE, $b^{\prime}𝑠$, and $\lambda^{\prime}𝑠$. However, this corresponds to the zero strain situation. For a zero stress (realistic conditions used in experiments) situtation a very small correction is found for the first anisotropy constant $\Delta K_1/K_1 = 0.07\%$, while a much more significant contribution is obtained for the second one $\Delta 𝐾_2/𝐾_2 = 21.86\%$. General analysis of this effect for tetragonal crystals is provided, finding that $\Delta 𝐾_1$ will be always positive for any stable phase with this symmetry [2]. We confront our magnetostriction coefficient with latest measurements for polycrystalline FePt.

Acknowledgements

The financial support of the projects QM4ST (CZ.02.01.01/00/22_008/0004572) by the Ministry of Education, Youth and Sports of the Czech Republic and No. 22-35410K of the Czech Science Foundation are acknowledged.

References

[1] T. Das et al., “Large magnetocrystalline anisotropic energy and its impact on magnetostriction of L10-FePt,” Journal of Physics D: Applied Physics, vol. 58, no. 3. IOP Publishing, p. 035004, Oct. 29, 2024. https://doi.org/10.1088/1361-6463/ad8001
[2] D. Legut, P. Nieves, "Second-order anisotropy due to magnetostriction for L1$_0$-FePt," Solid State Sciences, vol. 160. Elsevier BV, p. 107782, Feb. 2025. https://doi.org/10.1016/j.solidstatesciences.2024.107782

Speaker: Dr Dominik Legut (Charles University)

105 Magnetocaloric Effect in Binary Gd-Pb Alloys

The aim of present work was to study the phase composition, microstructure and magnetocaloric effect of binary Gd-Pb alloys. Samples were prepared by arc-melting of high purity constituent elements. The XRD studies were carried out using a Bruker D8 Advance diffractometer with Cu-K$\alpha$ radiation and semiconductor detector Lynx Eye. The microstucture and chemical composition of the samples were studied by scanning electron microscopy (SEM) using JEOL JSM 6610LV, equipped with an energy dispersive X-ray spectrometer (EDX). The XRD and SEM studies revealed biphasic structure built by pure Gd and secondary phase Gd-Pb. The magnetocaloric measurements revealed two maxima corresponding to two phases, which caused an increase of half width at half maximum of $\Delta$SM vs. $T$ curve. The analysis of the temperature dependence of magnetic entropy change allowed to construct temperature dependence of exponent $n$.

Speaker: Piotr Gębara (Department of Physics, Częstochowa University of Technology)

10:30 AM Coffee break

Section S6: Low-dimensional magnetic materials, molecular magnets and ferrofluids - PART 2

Convener: Ross Colman (Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University)

106 Manipulating Ground State Properties of a Large-D Spin-$1$ Chain System by Pressure

Magnetic order in gapped quantum antiferromagnets can be induced either by magnetic field or pressure. Such transitions are characterized by $z = 2$ or $z = 1$ dynamical critical exponents, determined by the quadratic or linear low-energy dispersion of their spin excitations, respectively. While the field-induced transitions (with the most common realization known as the Bose-Einstein magnon condensation) has been intensively studied, many details of the pressure-induced magnetic ordering has remained an open question. Employing high-pressure tunnel-diode-oscillator susceptibility, ultrasound, and high-field electron spin resonance spectroscopy measurements, we revealed pressure-induced magnetic ordering in the metal-organic material NiCl$_2\cdot 4$SC(NH$_2$)$_2$ (a.k.a. DTN), that we ascribe to the long-sought $z = 1$ criticality. This transition occurs at an easily accessible pressure of about $4.2$ kbar, allowing us to systematically study the low-temperature pressure-field phase diagram and establishing DTN as a perfect high-symmetry platform to investigate $z = 1$ quantum critical phenomena in solids.

Acknowledgements

The work was supported by the Deutsche Forschungsgemeinschaft as well as by HLD at HZDR, member of the European Magnetic Field Laboratory (EMFL).

References

[1] K. Yu. Povarov et al., “Pressure-tuned quantum criticality in the large-D antiferromagnet DTN,” Nature Communications, vol. 15, no. 1. Springer Science and Business Media LLC, Mar. 14, 2024. https://doi.org/10.1038/s41467-024-46527-x

Speaker: Sergei Zvyagin (Dresden High Magnetic Field Laboratory (HLD-HZDR))

107 Emergent Kasteleyn Signatures in Frustrated Quantum Heisenberg Antiferromagnets

We study the spin-$1/2$ Heisenberg antiferromagnet on a diamond-decorated honeycomb lattice and uncover a parameter regime in which the ground state corresponds to a dimer-tetramer crystal. In this regime, low-energy excitations are captured by an effective hard-dimer model on the honeycomb lattice with anisotropic activities. This effective model exhibits thermodynamic behavior consistent with Kasteleyn physics such as a sharp feature in the specific heat and quasi-long-range dimer correlations. Although the presence of monomers in the effective model precludes a rigorous proof of a finite-temperature phase transition [1], our large-scale simulations prove negligible monomer contribution in the relevant low-temperature regime indicating that the observed anomalous features stem from emergent dimer constraints enabling to approach Kasteleyn phase transition arbitrarily closely. These findings not only identify a concrete paradigmatic example of the quantum Heisenberg antiferromagnet realizing emergent Kasteleyn physics, but they open a route to uncover Kasteleyn signatures.

Acknowledgements

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie Grant Agreement No. 945380.

References

[1] O.J. Heilmann and E. H. Lieb, “Monomers and dimers,” Physical Review Letters, vol. 24, no. 25, pp. 1412–1414, June 1970. https://doi.org/10.1103/PhysRevLett.24.1412

Speaker: Katarina Karlova (Cergy Paris Universite, France)

108 Stimuli-Responsive Composites Incorporating Molecular Magnets and Organic Polymers

Recent scientific and technological efforts have increasingly focused on developing novel multifunctional materials whose properties can be dynamically tuned by external stimuli such as light, pressure, and electric or magnetic fields. Among these, organic-inorganic hybrid structures synthesized via simple wet-chemistry processes have emerged as promising candidates. Notably, materials exhibiting metal-to-metal charge transfer (MMCT) demonstrate inherent bistability and responsiveness, making them highly attractive for applications in molecular switches and sensors.

To enhance the processability and stability of these materials for practical integration into devices, a promising approach involves embedding functional frameworks within polymer matrices. This strategy transforms brittle crystalline materials into flexible polymeric composites while preserving their molecular functionality.

In our recent study, we investigated the multi-responsive, chain-like coordination compound {NH$_4$[Ni(cyclam)][Fe(CN)$_6$]$\cdot$5H$_2$O}$_n$ (where cyclam=$1$,$4$,$7$,$11$-tetraazacyclotetradecane). Although this compound exhibits limited stability, it undergoes a reversible thermal MMCT phase transition with bistability at room temperature, characterized by a sharp and broad thermal hysteresis loop [1]. By employing electrospinning, we successfully incorporated sub-micro and nanoparticles of this bistable material into poly($\varepsilon$-lactone) (PCL) and poly($2$-vinylpyridine-co-styrene) (P$2$VP-PS) fibers. Remarkably, the switchable properties were retained in the composite materials, as confirmed by optical observations and magnetic measurements. Moreover, the polymer matrix significantly enhanced the stability of the compound, broadening its potential applications as a temperature or pressure sensor.

Acknowledgements

This work was supported by the NCN within OPUS No. 2021/43/B/ST5/02216.

References

[1] M. Reczyński et al., “Room‐Temperature Bistability in a Ni–Fe Chain: Electron Transfer Controlled by Temperature, Pressure, Light, and Humidity,” Angewandte Chemie International Edition, vol. 60, no. 5. Wiley, pp. 2330–2338, Dec. 15, 2020. https://doi.org/10.1002/anie.202012876

Speaker: Magdalena Fitta (Institute of Nuclear Physics PAN)

Section S8: Strongly correlated electron systems, superconducting materials - PART 2

Convener: Ross Colman (Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University)

109 Upper Critical Field and Pairing Symmetry of Ising Superconductors

Several conflicting predictions have been made for the symmetry of the pairing in transition metal dichalcogenide (TMD) superconductors. An indication of whether singlet or triplet pairing is present can be given by the upper critical field ($H_{c}$), the magnetic field required to fully supress superconductivity. Monolayer 1H-NbSe$_{2}$ and 1H-TaS$_{2}$ have extremely large critical fields, due to a large Ising spin-orbit coupling (SOC) [1], yet their $H_{c}$ values do not scale with SOC and temperature as expected for other TMDs [2].

We will present our work [3], in which we highlight that the Ising SOC has nodal lines in the Brillouin zone imposed by symmetry. By deriving the susceptibility, we have found that the scaling of the critical field can be traced back to whether the Fermi surface intersects with these nodal lines or not. Reinterpreting existing experimental data, we find that only a predominantly singlet order is consistent with the values and the scaling of measured $H_{c}$ for several superconducting TMDs. Our analysis extends to multilayer TMDs, for which we will discuss the implications on the pairing symmetry.

References

[1] P. A. Frigeri, D. F. Agterberg, and M. Sigrist, “Spin susceptibility in superconductors without inversion symmetry,” New J. Phys., vol. 6, pp. 115–115, Sep. 2004, https://doi.org/10.1088/1367-2630/6/1/115.
[2] S. C. de la Barrera et al., “Tuning Ising superconductivity with layer and spin–orbit coupling in two-dimensional transition-metal dichalcogenides,” Nat Commun, vol. 9, no. 1, Apr. 2018, https://doi.org/10.1038/s41467-018-03888-4
[3] L. Engström, L. Zullo, T. Cren, A. Mesaros, and P. Simon, “Upper critical field and pairing symmetry of Ising superconductors,” 2025, arXiv. https://doi.org/10.48550/ARXIV.2504.20775

Speaker: Prof. Tristan Cren (Sorbonne University, Paris, FR)

110 Single-Gap Two-Band Superconductivity Well Above the Pauli Limit in Non-Centrosymmetric TaIr$_2$B$_2$

Non-centrosymmetric superconducting materials represent an exciting class of novel superconductors featuring a variety of unconventional properties, including mixed-parity pairing and very high upper critical fields. Here, we present a comprehensive study of TaIr$_2$B$_2$ (with $T_c = 5.1$ K), using a set of complementary experimental methods, including bulk- and surface-sensitive techniques. We provide evidence that this system is a two-band, yet it behaves as a single-gap superconductor with a strong coupling. The upper critical field of TaIr$_2$B$_2$ significantly exceeds the Pauli limit and exhibits a nearly linear temperature dependence down to the lowest temperatures. This behavior, rarely seen in superconductors, is discussed in terms of anti-symmetric spin-orbit interaction, two-band-, and strong-coupling effects, as well as disorder.

Acknowledgements

The work at Gdansk University of Technology was supported by the National Science Center (Poland), Grant No. 2022/45/B/ST5/03916. The work at Slovak Academy of Sciences was supported by Projects APVV-23–0624, VEGA 2/0073/24, COST Action No. CA21144 (SUPERQUMAP), Slovak Academy of Sciences Project IMPULZ IM-2021–42. We acknowledge the support of LNCMI-CNRS, member the European Magnetic Field Laboratory (EMFL). A portion of this work was performed at the National High Magnetic Field Laboratory, which is supported by National Science Foundation Cooperative Agreement No. DMR-1644779 and the State of Florida.

Speaker: Dr Jozef Kačmarčík (Centre of Low Temperature Physics, Institute of Experimental Physics, Slovak Academy of Sciences)

12:45 PM LUNCH

Section S9: Multifunctional magnetic materials (multiferroic, magnetoelastic, shape memory, …)

Convener: Piotr Gębara (Department of Physics, Częstochowa University of Technology)

111 Artificial Magnetoelectric Multiferroic Thin Films Combining Ferrites and Barium Titanate: Magnetism vs. Structure

Artificial magnetoelectric multiferroic heterostructures, which combine multiple ferroic orders, have high potential for next-generation electronic devices. With device downscaling, the interface plays an increasingly important role and deserves special consideration. Oxide films are especially well suited for such applications. We combined Co [1] and Ni [2] ferrite layers, which bring their ferrimagnetic long range order with pure and N-doped barium titanate, which is a cost-effective and environment friendly prototypical ferroelectric material.

All layers were grown epitaxially using plasma assisted molecular beam epitaxy. Oxygen plasma was used to grow the ferrite layers and pure BaTiO$_3$. We employed an original approach consisting in using the SrTiO$_3$(001) substrate as the oxygen supplier and atomic nitrogen plasma to incorporate a small amount of substitutional N atoms into the BaTiO$_3$ perovskite lattice [3, 4]. The layers were thoroughly characterized by in situ high energy electron diffraction, Auger and photoemission spectroscopies analysis and ex situ by piezo-force and high-resolution electron microscopies. More detailed investigations were conducted using synchrotron radiation and in particular X-ray diffraction and X-ray magnetic circular dichroism.

On pure oxide systems, we could determine the correlation between these properties with respect to the respective layer thicknesses. Although Co and Ni ferrites are close compounds, we obtain different behaviours in the very thin film regime when deposited on BaTiO$_3$. Ni ferrite shows an almost magnetic dead layer below $4$ nm and different growth strain. We could determine annealing conditions allowing to cure the lack of magnetism for the thin films [2] which is understood as due to the imperfect formation of the Ni ferrite spinel structure.

A comparative study of CoFe$_2$O$_4$ grown on pristine and N-doped BaTiO$_3$ demonstrates different plastic relaxation leading to substantial changes in the magnetic properties of the ferrite overlayer showing that N-doping can be used as a tuning parameter in multiferroics [5].

Acknowledgements

The authors gratefully acknowledge the “Agence Nationale de la Recherche (ANR)” for their funding through the MULTINANO project (grant no. ANR-19-CE09-0036).

References

[1] N. Jedrecy et al., “Cross-Correlation between Strain, Ferroelectricity, and Ferromagnetism in Epitaxial Multiferroic CoFe2O4/BaTiO3 Heterostructures,” ACS Applied Materials & Interfaces, vol. 10, no. 33. American Chemical Society (ACS), pp. 28003–28014, Aug. 07, 2018. https://doi.org/10.1021/acsami.8b09499
[2] H. Lin et al., “Unveiling and Optimizing Interface Properties of NiFe2O4/BaTiO3 Heterostructures,” ACS Applied Electronic Materials, vol. 6, no. 10. American Chemical Society (ACS), pp. 7286–7300, Oct. 10, 2024. https://doi.org/10.1021/acsaelm.4c01215
[3] A. Derj et al., “Properties of self-oxidized single crystalline perovskite N : BaTiO3 oxynitride epitaxial thin films,” Materials Advances, vol. 3, no. 7. Royal Society of Chemistry (RSC), pp. 3135–3142, 2022. https://doi.org/10.1039/d1ma01082d
[4] C. Blaess et al., “Nitrogen Doping in Epitaxial Self-Oxidized BaTiO3 Ferroelectric Thin Films,” The Journal of Physical Chemistry C, vol. 129, no. 7. American Chemical Society (ACS), pp. 3849–3861, Feb. 11, 2025. https://doi.org/10.1021/acs.jpcc.4c07538
[5] C. Blaess et al., “Manipulation of artificial multiferroics using doping-induced plastic strain relaxation,” Applied Surface Science, vol. 690. Elsevier BV, p. 162585, May 2025. https://doi.org/10.1016/j.apsusc.2025.162585

Speaker: Dr Antoine Barbier (Université Paris-Saclay, CEA, CNRS, SPEC)

112 Progress in Understanding Magnetic Shape Memory Effects

In my presentation I will review the latest progress in understanding elastomagnetic multiferroic behavior of Ni-Mn-Ga Heusler alloys called magnetic shape memory effects [1]. These phenomena are underlined by displacive and diffusionless phase transformation from cubic to lower symmetry phase called martensitic transformation. Apart from temperature the transformation can be induced by magnetic field, and this usually provides large field induced stress, but the main merit is for magnetocaloric applications. The field induced transformation is not strictly multiferroic as only magnetization difference between phases is needed. The effect usually requires large magnetic field of order several Teslas.

The other effect is magnetically induced (structural) reorientation (MIR) providing giant, up to $12\%$ deformation in moderate magnetic field. The effect takes place in single ferromagnetic phase after martensitic transformation establishing ferroelastic order. Coupling between ferromagnetic and ferroelastic order is provided by large magnetocrystalline anisotropy. Together with high mobility of twin interfaces or very low twinning stress compared to other shape memory alloys these provide necessary conditions for the effect.

Here I will focus on new recent discoveries concerning MIR in Ni-Mn-Ga. I will examine material demands; in particular the partial doping of Ni-Mn-Ga by transition metals in attempt to increase transformation temperatures, the twin hierarchy from macro to nanoscale important for twin mobility, and recently discovered extreme shear instability of the lattice, which may be a key for the supermobility of twin boundaries [2]. Moreover, the nature of antiphase boundaries in ordered Heusler alloys, which can enhance the functionalities of the material, will be discussed. All these characteristics observed experimentally will be put to the perspective of theoretical calculation which is still regrettably not to date for such interesting materials [3]. From experimental point of view the phenomenology of the effect is well known, however, the underlining physical principles and the role of magnetism in the existence of modulated structures is not clear.

Acknowledgements

We thank for support OP JAK Ferroic Multifunctionalities No. CZ.02.01.01/00/22_008/0004591 and GAČR No. 23-04806S projects.

References

[1] O. Heczko et al., “Coupling between ferromagnetic and ferroelastic transitions and ordering in Heusler alloys produces new multifunctionality,” MRS Bulletin, vol. 47, no. 6. Springer Science and Business Media LLC, pp. 618–627, Jun. 2022. https://doi.org/10.1557/s43577-022-00354-x
[2] K. Repček et al., “Compliant Lattice Modulations Enable Anomalous Elasticity in Ni–Mn–Ga Martensite,” Advanced Materials. Wiley, Aug. 12, 2024. https://doi.org/10.1002/adma.202406672
[3] H. Seiner et al., “Experimental Observations versus First‐Principles Calculations for Ni–Mn–Ga Ferromagnetic Shape Memory Alloys: A Review,” physica status solidi (RRL) – Rapid Research Letters, vol. 16, no. 6. Wiley, Mar. 30, 2022. https://doi.org/10.1002/pssr.202100632

Speaker: Oleg Heczko (FZU - Institute of Physics of the Czech Academy of Sciences)

113 Temperature- and Composition-Driven Structural and Magnetic Transitions in High-Pressure Stabilized Perovskites Based on BiFeO$_3$

Chemical modifications in the iron site of BiFeO$_3$ represent the direct approach to tune the magnetic behaviour of this material. However, using the conventional synthesis routes, it is possible to achieve the substitution rates of a few atomic percent only. Most of the reported single-phase BiFe$_{1−y}$B$^{3+}_{y}$O$_3$ perovskite compositions with $y > 0.1$ were prepared via high-pressure synthesis.

In high-pressure stabilized perovskite solid solutions of the BiFe$_{1−y}$Sc$_y$O$_3$ system, a series of structural transitions with increasing $y$ was found. Moreover, it was revealed that annealing of the as-prepared perovskite phases results in irreversible transformations into new structural phases with interesting combinations of ferroic orders [1]. In the $0.1 \leq y < 0.3$ range, some peculiarities of the temperature-dependent magnetic moment below $T_N$ were observed and associated with possible transitions between different antiferromagnetic structures corresponding to collinear, canted, and cycloidal spin arrangements [2]. Similar temperature anomalies of the magnetic behaviour below $T_N$ were then revealed in the Fe-rich compositional range of the BiFe$_{1−y}$[Zn$_{0.5}$Ti$_{0.5}$]$_y$O$_3$ perovskites [3].

We present the temperature and compositional behaviours of the crystal structure and the magnetic properties of the BiFe$_{1−y}$B$^{3+}_{y}$O$_3$ perovskites (where B$^{3+}$ = Ga, Co, Mn, Cr, [Zn$_{0.5}$Ti$_{0.5}$] and Sc) in the vicinity of parent bismuth ferrite. Among these, Cr$^{3+}$, Mn$^{3+}$, and Co$^{3+}$ are magnetic cations of transition metals from the same 3d series to which iron belongs, while Ga$^{3+}$, Sc$^{3+}$ and [Zn$_{0.5}$Ti$_{0.5}$]$^{3+}$ are non-magnetic. Besides, as compared with iron, gallium is smaller, scandium is considerably bigger, and [Zn$_{0.5}$Ti$_{0.5}$]$^{3+}$ is slightly bigger than Fe$^{3+}$ in octahedral coordination. The crystal structure sequences, phase diagrams and the $T_N(y)$ dependences are compared and discussed.

References

[1] D. D. Khalyavin et al., “The phenomenon of conversion polymorphism in Bi-containing metastable perovskites,” Chemical Communications, vol. 55, no. 32. Royal Society of Chemistry (RSC), pp. 4683–4686, 2019. https://doi.org/10.1039/c9cc00472f
[2] E. L. Fertman et al., “Magnetic Diagram of the High-Pressure Stabilized Multiferroic Perovskites of the BiFe1-yScyO3 Series,” Crystals, vol. 10, no. 10. MDPI AG, p. 950, Oct. 17, 2020. https://doi.org/10.3390/cryst10100950
[3] A. N. Salak et al., “Magnetic Behaviour of Perovskite Compositions Derived from BiFeO3,” Magnetochemistry, vol. 7, no. 11. MDPI AG, p. 151, Nov. 16, 2021. https://doi.org/10.3390/magnetochemistry7110151

Speaker: Andrei Salak (University of Aveiro)

114 Broadband Ferromagnetic Resonance in Ni-Mn-Ga Single Crystal

Ferromagnetic resonance (FMR) is a unique technique used to determine fundamental properties of the studied magnetic material, such as magnetocrystalline anisotropy, $g$-factor, exchange constant, Gilbert damping, etc. in single crystals (SCs) or magnetic interactions between layers and components in multilayered nanostructured films and foils [1]. Ni-Mn-Ga Heusler alloys are a subclass of traditional shape memory materials that exhibit strains and shape change not only in response to the increase of temperature but also when exposed to relatively low ($<5$ kOe) external magnetic field. These alloys, called magnetic shape memory (MSM) alloys, are known for large reversible magnetic-field-induced strain (MFIS) of up to $12\%$ while staying in their martensitic phases ($10$M, $14$M and NM). FMR in epitaxially grown Ni-Mn-Ga thin films, where the twin structures are confined by the rigid substrate, has been thoroughly investigated, e.g. in [2]. On the contrary only a few papers exist on FMR in SC MSM alloys. The temperature and angular dependences of FMR were previously measured on bulk Ni-Mn-Ga SCs at X-band microwave frequency [3]. However, the derived anisotropy constants substantially differed from those determined from the magnetization measurements.

Here we present a broadband ferromagnetic resonance study in SC Ni$_{50}$Mn$_{28.1}$Ga$_{21.9}$ in the temperature range from $20$ °C to $140$ °C in which the martensite transformation occurs. Our results demonstrate that a large change (an order of magnitude) in the magnetocrystalline anisotropy at the martensitic phase transformation results in a sharp change of the resonance magnetic field. In a single variant martensite phase the resonance fields satisfy the Kittel’s resonance condition for a thin film with the gyromagnetic factor $g=2.0$. With the magnetic field parallel to the easy $c$-axis of the single variant martensite the resonance is observed only for frequencies larger than $22$ GHz. For the multivariant martensite case we considered the magnetic coupling between the twin variants for the satisfactory Kittel’s fit. We observe a week magnetocrystalline anisotropy in the austenite phase, comparable to the previous reports based on different magnetic measurements.

Acknowledgements

The authors acknowledge the support of OP JAK project No. CZ.02.01.01/00/22_008/0004591 and CSF grant No. 22-22063S.

References

[1] O. Yaln, Ed., “Ferromagnetic Resonance - Theory and Applications.” InTech, Jul. 31, 2013. https://doi.org/10.5772/50583
[2] P. V. Bondarenko et al., “Giant four-fold magnetic anisotropy in nanotwinned NiMnGa epitaxial films,” APL Materials, vol. 11, no. 12. AIP Publishing, Dec. 01, 2023. https://doi.org/10.1063/5.0162561
[3] V. G. Gavriljuk et al., “A study of the magnetic resonance in a single-crystal Ni50.47Mn28.17Ga21.36alloy,” Journal of Physics: Condensed Matter, vol. 18, no. 32. IOP Publishing, pp. 7613–7627, Jul. 31, 2006. https://doi.org/10.1088/0953-8984/18/32/010

Speaker: Dr Denys Musiienko (FZU - Institute of Physics of the Czech Academy of Sciences)

115 Stabilization of I-type Ni$_4$Nb$_2$O$_9$ Structure and Magnetic Properties in Ni$_4$Nb$_{1.8}$W$_{0.1}$Ti$_{0.1}$O$_9$

The A$_4$M$_2$O$_9$ family (A = divalent cations; M = Nb/Ta), which typically adopts a trigonal P$\overline{3}c$1 structure derived from corundum, exhibits magnetoelectric (ME) properties in antiferromagnetic compounds such as Co$_4$Nb$_2$O$_9$. Ni$_4$Nb$_2$O$_9$ stands out as an exception, crystallizing in a different but close structure described in the orthorhombic $Pbcn$ space group that is ferrimagnetic and does not show ME activity. Here, we demonstrate how Ti$^{4+}$/W$^{6+}$ co-substitution on Nb$^{5+}$ sites stabilizes a superstructure derived from $Pbcn$ and described in the polar I-type $Fdd2$ space group for Ni$_4$Nb$_{1.8}$W$_{0.1}$Ti$_{0.1}$O$_{9}$. This structural study that combines synchrotron X-ray and neutron diffraction data with electron microscopy reveal a strongly distorted corundum-like framework. Magnetic characterizations were performed by DC and AC-susceptibility measurements, showing a ferrimagnetic transition at 68 K, followed by a re-entrant spin-glass-like state below $\approx$ 50 K. The magnetic structure is established by neutron diffraction, evidencing a collinear ferrimagnetic structure.

Acknowledgements

We thank CELLS-ALBA for synchrotron access, CANAM/NPI CAS Řež for neutron diffraction facilities (MEYS LM2023041), and the Nord-Pas de Calais Regional Council/ERDF for supporting the Lille TEM facility.

Speaker: Charles Hervoches (Nuclear Physics Institute of the Czech Academy of Sciences)

4:00 PM Coffee break

Section S2: Amorphous, nanocrystalline and other soft magnetic materials - PART 2

Convener: Dr Ivan Škorvánek (Institute of Experimental Physics, Slovak Academy of Sciences)

116 Manganese-Zinc Ferrites: Material Design Challenges and Development Approaches Towards Advanced Applications

The industrial production of advanced Mn-Zn ferrites often faces unique challenges that determine its upscaling success. These range from controlling fundamental properties such as thermal expansion to meeting broader goals of innovation and sustainability. The present work aims to address key material design challenges and strategic development approaches to these goals.

One of the critical cost factors of Mn-Zn ferrite production is the loading efficiency of the sintering furnaces. However, the thermal expansion of the ferrite during the early stages of sintering may cause sticking of the neighbouring ferrite cores, if positioned too close on the sintering plate. To minimize this risk, a systematic investigation of the expansion characteristics of Mn-Zn ferrites of various Zn contents was done, in relation to the atmosphere during prefiring and sintering. Phase identification during the two thermal processes, combined with their magnetic response, led to the determination of the optimal temperature and atmosphere parameters to avoid product sticking while preserving optimal magnetic performance.

Beyond conventional ferrite core production, however, innovation through the development of ferrite powders is in growing demand, aiming to exploit their inductive performance in the design of thermally activated processes and applications, as at the micro range, the ferrite particles are multi-domain, exhibiting intra-particle domain walls. The primary goal being to establish a correlation between the magnetic performance of sintered cores and powders, Mn-Zn and Mg-Mn ferrite materials were prepared following the ceramic method and were structurally, morphologically and magnetically characterized. A direct correlation between the two states was achieved through $B$-$H$ loop acquisition and VSM measurements, while the heating ability of the prepared powders provided further insights. Several granulation techniques shed light on the flexibility of ferrite powders in terms of granulate size and inductive response.

Regardless of specific application requirements, sustainability has become a fundamental priority in modern industrial production, driving the need for resource-efficient materials. In this context, a high-value spinel Mn-Zn ferrite was successfully developed through the targeted conversion of an industrial solid waste, electrolytic MnO$_2$. Material design was based on the optimal treatment of the waste starting from constituents’ separation, combined with a proper process design to fit the conventional ceramic technique and a targeted compositional adjustment. The lab-developed Mn-Zn ferrite was upscaled to a semi-pilot plant for tile-shaped products, which were successfully implemented as magnetic shielding couplers on a prototype wireless charging unit. The achieved $23\%$ increase in the current intensity flow demonstrates the potential of circular economy principles in advancing sustainable ferrite technology.

Speaker: Dr Vasiliki Tsakaloudi (Centre for Research and Technology-Hellas CERTH)

117 Influence of Stress-Induced Anisotropy on the Local Atomic Structure of Fe$_3$Si Nanocrystals

Many technological applications require low permeability of a few hundreds being constant over a wide magnetic field range. For example, this is a case of magnetic energy storage cores [1]. It is well known that magnetic anisotropy induced by stress applied during annealing can reach magnitudes up to several thousands of J/m$^3$ which is about two orders of magnitude larger than the magnetic anisotropy induced by annealing in a magnetic field [2]. Furthermore, stress induced anisotropy (SIA) represents an effective way to tailor magnetic characteristics of nanocrystalline Vitroperm-like alloy systems. It was shown that the SIA has its origin in magneto-elastic anisotropy of the Fe-Si crystallites associated with their elongation induced by stress annealing [3]. Our recent results obtained by mapping out the strain pole figures (SPF) corresponding to several Bragg reflections of Fe$_3$Si cubic phase show that SIA is actually uniaxial and its main axis is aligned along tensile direction. Furthermore, SPFs provided evidence that strain partitioning among different Bragg reflections is not even and the magnitude of the SIA for a given set of Bragg reflections is inversely proportional to its Young’s modulus $E_{hkl}$.

The main goal of this study was to analyze the impact of the SIA on a local atomic structure of Fe$_3$Si nanocrystals. High-Resolution Transmission Electron Microscopy (HR-TEM) combined with Pair Distribution Function (PDF) technique were employed to address such a delicate topic. PDF provided evidence that the bond length distributions corresponding to the nearest-neighbors environments of Fe$_{3}$Si cubic phase are reflecting direction of applied tensile stress. When observing PDF along tensile direction, shifts towards larger $r$-values are observed for all coordination shells up to $2$ nm. An opposite behavior is seen in transversal direction. HR-TEM analysis of several individual grains having different crystallographic orientations reveals different extent of change in interplanar spacings depending on Fe$_3$Si crystal orientation with respect to direction of applied stress.

Acknowledgements

This study was funded by the EU NextGenerationEU through the Recovery and Resilience Plan for Slovakia under the project No. 09I03-03-V03-00034.

References

[1] H. Fukunaga et al., “Nanostructured soft magnetic material with low loss and low permeability,” Journal of Applied Physics, vol. 87, no. 9. AIP Publishing, pp. 7103–7105, May 01, 2000. https://doi.org/10.1063/1.372944
[2] M. Ohnuma et al., “Origin of the magnetic anisotropy induced by stress annealing in Fe-based nanocrystalline alloy,” Applied Physics Letters, vol. 86, no. 15. AIP Publishing, Apr. 08, 2005. https://doi.org/10.1063/1.1901807
[3] D. Yudina et al., “Structural aspects of stress-induced magnetic anisotropy in Fe-based nanocrystalline alloy,” Journal of Alloys and Compounds, vol. 960. Elsevier BV, p. 171011, Oct. 2023. https://doi.org/10.1016/j.jallcom.2023.171011

Speaker: Dr Jozef Bednarčík (Pavol Jozef Šafárik University in Košice, Faculty of Science, Institute of Physics)

118 Neutron Irradiation Effects on Fe-Based Metallic Glasses

Metallic glasses (MGs) are promising materials for radiation-resistant applications due to their disordered atomic structure and excellent magnetic properties. This study examines the effects of neutron irradiation (fluence up to $3\times10^{16}$ $cm^{−2}$) on Fe-based metallic glasses using Mössbauer spectroscopy (MS) and X-ray diffraction (XRD).

XRD analysis, particularly total scattering factor $S(q)$ and pair distribution function $G(r)$, revealed only minor changes, suggesting that the overall atomic arrangement remained largely preserved. However, Mössbauer spectroscopy detected subtle structural modifications, as evidenced by changes in hyperfine field distributions and the orientation of the net magnetic moment. These observations indicate that even relatively low neutron fluence can induce localized atomic rearrangements, which could influence the material’s magnetic properties.

When compared to previous studies [1], which investigated neutron irradiation effects at fluences up to $10^{19}$ $cm^{−2}$, our results suggest that structural modifications can be observed even at much lower fluences. This highlights the high sensitivity of Mössbauer spectroscopy in detecting irradiation-induced effects in metallic glasses.

The findings contribute to understanding the radiation tolerance of Fe-based metallic glasses and their potential for applications in radiation-exposed environments.

Acknowledgements

This work was supported by the Large Research Infrastructures of the Ministry of Education, Youth and Sports of the Czech Republic no. LM2023073 and by the project VEGA 1/0010/24. This study was co-funded by the EU NextGenerationEU through the Recovery and Resilience Plan for Slovakia under the project No. 09I03-03-V03-00034.

References

[1] M. B. Miglierini, “Radiation Effects in Amorphous Metallic Alloys as Revealed by Mössbauer Spectrometry: Part I. Neutron Irradiation,” Metals, vol. 11, no. 5. MDPI AG, p. 845, May 20, 2021. https://doi.org/10.3390/met11050845

Speaker: Dr Martin Cesnek (Department of Nuclear Reactors, Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague)

POSTER Session: PART 2 (Topics 1, 4, 6, 7, 8 and 10)

Conveners: Prof. Pavol Sovák (Pavol Jozef Šafárik University in Košice, Faculty of Science, Institute of Physics), Dr Adriana Zeleňáková (Pavol Jozef Šafárik University in Košice, Faculty of Science, Institute of Physics)

119 Bistable Microwire Usage as the Sensor for Single Chip Applications

Magnetic bistable microwires represent a highly promising technology in the field of sensor and actuator electronic systems. Their unique properties are well known within the scientific community as well as in practical applications and have been widely discussed. Microwires with an amorphous structure exhibit not only a high magnetoimpedance response but also the ability to detect extremely weak magnetic fields, making them suitable for use in biometric and medical sensors, industrial measurement systems, and intelligent IoT devices. Additionally, these microwires can be used to directly sense another physical quantities, such as temperature and mechanical stress. Thanks to these sensing properties, bistable microwires are applicable in a wide range of applications while providing highly accurate results.

Depending on the application and the magnitude of the excitation field required for microwires, the simplest system configuration can utilize a miniature coil assembly consisting of one excitation coil and one sensing coil, along with electronics that can be largely integrated into commonly available microcontrollers designed for digital signal processing (DSP processors).

Research in the field of magnetic bistable microwires and electronics focuses on optimizing microwire placement and system design to achieve maximum sensitivity and stability using only a DSP processor and a few essential electronic components. Magnetic bistable microwires used in single-chip applications require optimized integration with microelectronics and advanced signal processing technologies.
This work presents the application of bistable microwires in a new compact configuration of electronic components and the STM$32$G$474$RE microcontroller, which includes a full set of instructions for digital signal processing. These hardware components, together with the coil system and the microwire, form a miniature embedded sensor for measuring temperature, mechanical stress, and magnetic fields. Thanks to the excellent properties of magnetic bistable microwires, all these parameters can be measured in real time with high sensitivity. The microwire response is represented as a voltage peak, which can be measured and processed using integrated ADCs or analog comparators. The key innovation compared to previous configurations presented in [1,2] is absolute miniaturization and the full utilization of the microcontroller's capabilities for managing and processing the signal from the bistable microwire.

References

[1] P. Jacko et al., “Linear position sensor using magnetically bistable microwire,” Sensors and Actuators A: Physical, vol. 349. Elsevier BV, p. 114017, Jan. 2023. https://doi.org/10.1016/j.sna.2022.114017
[2] P. Jacko et al. “Advantages of Bistable Microwires in Digital Signal Processing,” Sensors, vol. 24, no. 8. MDPI AG, p. 2423, Apr. 10, 2024. https://doi.org/10.3390/s24082423

Speaker: Dr Patrik Jacko (RVmagnetics, a.s., Nemcovej 30, 040 01 Kosice, Slovakia)

120 Coexistence of Quantum Tunnelling and Anomalous Raman Relaxation in {[Ce$_2$($o$PDA)$_3$(H$_2$O)$_2$]$\cdot$2H$_2$O}$_n$

Structural, static and dynamic magnetic properties of title complex {[Ce$_2$($o$PDA)$_3$(H$_2$O)$_2$]$\cdot 2$H$_2$O}$_n$ containing O-donor ligand H$_{2o}$PDA ($o$-phenylenediacetic acid) are reported. The structure of the studied compound is formed by chains of the Ce$^{3+}$ ions linked via $o$PDA$^{2-}$ dianions which act as pentadentate ligands with bridging and chelating functions. The analysis of the temperature dependence of the effective magnetic moment enabled to estimate the energy difference between the ground and the first excited doublet $\Delta/k_B= 317$ K. Large energy separation between the two doublets was also confirmed by the evaluation of magnetic field dependence of the magnetization studied up to $5$ T at $2$ K, $5$ K and $10$ K. Persistence of quantum tunnelling at $3.5$ K up to $0.7$ T revealed by studying magnetic field dependence of the relaxation time was attributed to powder nature of the sample. Investigation of Cole-Cole diagrams supported the dominance of Debye-like relaxation suggesting rather narrow distribution of the relaxation times. Temperature dependences of the relaxation time from $2$ K to $6$ K in magnetic fields $0.1$ T and $0.35$ T were explicable assuming the coexistence of quantum tunnelling and anomalous Raman relaxation with $\tau\approx T^{5.6}$ in striking difference with $n=7$ or $n=9$ which is expected for standard Raman relaxation of non-Kramers or Kramers ions with well separated doublets. The obtained results can be interpreted assuming the coexistence of standard Raman process and the coupling of Ce$^{3+}$ ions with low-energy local vibrational modes, the latter interaction was recently proposed as governing relaxation mechanism in several Ce(III) based metal-organic frameworks [1].

Acknowledgements

This work was supported by Slovak research agency under contract APVV-22-0172 and by the EU NextGenerationEU through the Recovery and Resilience Plan for Slovakia under the project No. 09I03-03-V04-00176.

References

[1] J. Torrent et al., “Cerium-Based Metal–Organic Frameworks: Unveiling the Role of Terahertz Vibrations in the Spin Relaxation Dynamics,” Inorganic Chemistry, vol. 64, no. 8. American Chemical Society (ACS), pp. 3735–3746, Feb. 18, 2025. https://doi.org/10.1021/acs.inorgchem.4c04542

Speaker: Prof. Martin Orendáč (Institute of Physics, Faculty of Science, P. J. Šafárik University in Košice)

121 Consolidated Fe/FeSi Mixtures for Applications Requiring Increased Frequency Stability of Magnetic Properties

Mixing powder materials with distinct properties is a well-established approach to overcoming the limitations of individual powders. In soft magnetic systems, this strategy enhances the compressibility of high-performance but brittle materials, such as FeSi [1], FeSiB [2], and FeSiBCCr [3]. FeSi with $>3$ wt.$\%$ Si is typically mixed with epoxy binders, restricting high-temperature processing and limiting its soft magnetic applications.

This study investigates Fe-$6.5$Si/Fe composites with a phosphate surface layer, focusing on the effects of Fe/FeSi ratios, process additives, and compaction parameters on magnetic properties. Fe-$6.5$Si and Somaloy $700$ (Höganäs AB) were used. Somaloy $700$ (without lubricant) was treated with KH550 surfactant ($6$ wt.$\%$), homogenized with FeSi in ethanol via resonant acoustic mixing (RAM), dried ($60$°C, $3$ hrs.), and uniaxially pressed ($800$ MPa) into cylinders and rings. Heat treatments were performed at $650$°C/$1$ hr. and $700$°C/$5$ min. in N$_2$. Similarly, Somaloy $700$ (with lubricant) was RAM-mixed with FeSi, pressed at 800 and $1500$ MPa, and heat-treated at identical conditions in air.

Resistivity increased with FeSi content in silanized Fe/FeSi, reaching $1.43\times10^{-1}$ $\Omega$cm at $50:50$, while a lubricant-based counterpart achieved only $4.0\times10^{-4}$ $\Omega$cm ($800$ MPa) and $2.46\times10^{-4}$ $\Omega$cm ($1500$ MPa). The highest real permeability ($\mu^{\prime}=72$) was observed in silanized Fe/FeSi $70:30$, whereas pure FeSi exhibited the highest relaxation frequency ($4.2$ MHz, $\mu^{\prime}=57$). Lubricant-enhanced samples achieved higher permeability ($198$ for Fe/FeSi $70:30$ at $1500$ MPa). A $60:40$ Fe/FeSi mix ($800$ MPa) had a relaxation frequency of $12.5$ kHz ($\mu^{\prime}=140$), which decreased to $4.8$ kHz ($\mu^{\prime}=180$) at $1500$ MPa for the $50:50$ composition.

Coercivity trends differed between silanized and lubricated samples. In silanized materials, coercivity decreased with increasing FeSi, reaching 210 A/m at Fe/FeSi 50:50 and 130 A/m for pure FeSi. In contrast, lubricated Fe/FeSi 70:30 exhibited $\sim$300 A/m, and 50:50 reached 350 A/m. These results highlight distinct structure formation mechanisms in lubricant- vs. silane-treated compacts, influencing their functional properties. The findings offer new insights into optimizing Fe and FeSi materials for industrial soft magnetic applications.

Acknowledgements

This work was realized within the frame of the project VEGA 2/0099/24.

References

[1] Z. Zheng et al., “Magnetic properties regulation and loss contribution analysis of FeSi soft magnetic composites doped by carbonyl iron powders,” Journal of Magnetism and Magnetic Materials, vol. 568. Elsevier BV, p. 170423, Feb. 2023. https://doi.org/10.1016/j.jmmm.2023.170423
[2] D. N. Chen et al., “Improving the Magnetic Properties of FeSiB Soft Magnetic Composites by Adding Untreated or Phosphated Fe Powders,” Journal of Magnetics, vol. 24, no. 3. The Korean Magnetics Society, pp. 485–490, Sep. 30, 2019. https://doi.org/10.4283/jmag.2019.24.3.485
[3] J. Liu et al., “Improved high-frequency magnetic properties of FeSiBCCr amorphous soft magnetic composites by adding carbonyl iron powders,” Journal of Non-Crystalline Solids, vol. 605. Elsevier BV, p. 122166, Apr. 2023. https://doi.org/10.1016/j.jnoncrysol.2023.122166

Speaker: Soundariya Ravi (Institute of Materials Research, Slovak Academy of Sciences)

122 Development of Fractional Magnetization Plateaus in Metallic Quasi-$2$ Dimensional Shastry-Sutherland System TmB$_4$ at Various Orientations and in High Magnetic Fields

The metallic tetraboride TmB$_4$ is one of the best-known representatives of Shastry-Sutherland lattice (SSL), which is a two-dimensional geometrically frustrated lattice [1]. The long-range Ruderman-Kittel-Kasuya-Yosida (RKKY) exchange interaction between magnetic moments leads to antiferromagnetic (AF) ordering of dimers. Crystal field effect at Tm$^{3+}$ ion sites leads to strong Ising anisotropy along the $c$ axis, thus allowing the manifestation of the SSL in the $a$-$b$ plane, which is reflected by the fact that the magnetic field of saturation $H_{sat}$ along the $c$ axis is at least 10 times smaller than this in the perpendicular $a$-$b$ plane direction [2]. The magnetization $M$ along the $c$ axis exhibits the fractional magnetization plateaus (FMPs) with $M/M_{sat}$ = $1/11$, $1/9$, $1/8$ and $1/7$, where $M_{sat}$ is the saturation magnetization, in fields between $14$ kOe and $17.5$ kOe [1]. Half plateau with $M/M_{sat}=1/2$ arises between $17.5$ kOe and $36$ kOe. However, there is very little known about the development of FMPs, when the applied field $H$ deviates from $c$ axis and becomes parallel to $a$-$b$ plane. Up to now, there were only two $M(H)$ measurements for $H\perp c$ [2, 3], which show the saturation field of $H_{sat}\approx400$ kOe for $H \parallel [100]$ [2, 3] and different behavior of $M(H)$ with $H_{sat} > 550$ kOe for $H \parallel [110]$ [3], respectively. Within this work, we investigate the $M(H,\phi,T)$ angular development of FMPs in TmB$_4$ up to $600$ kOe (from $H \parallel c$ to $H \parallel [100]$ and from $H\parallel c$ to $H \parallel [110]$). The obtained results provide a new complex view on the FMPs in this material, which will allow the development of new (necessary) theoretical approaches of the metallic SSL.

Acknowledgements

This work was supported by projects APVV-23-0226, VEGA 2/0034/24, DAAD-SAS-2023-02. We acknowledge the support of the HLD-HZDR, member of the European Magnetic Field Laboratory (EMFL). M.O. acknowledges the support of the NextGenerationEU through the Recovery and Resilience Plan for Slovakia under the project No. 09I03-03-V04-00304.

References

[1] K. Siemensmeyer et al., “Fractional Magnetization Plateaus and Magnetic Order in the Shastry-Sutherland Magnet TmB$_4$”,Physical Review Letters, vol. 101, no. 17. American Physical Society (APS), Oct. 20, 2008. https://doi.org/10.1103/physrevlett.101.177201
[2] F. Iga et al., “Highly anisotropic magnetic phase diagram of a 2-dimensional orthogonal dimer system TmB4,” Journal of Magnetism and Magnetic Materials, vol. 310, no. 2. Elsevier BV, pp. e443–e445, Mar. 2007. https://doi.org/10.1016/j.jmmm.2006.10.476
[3] S. Yoshii et al., “High-field magnetization of TmB4,” Journal of Physics: Conference Series, vol. 51. IOP Publishing, pp. 59–62, Nov. 01, 2006. https://doi.org/10.1088/1742-6596/51/1/011

Speaker: Dr Matúš Orendáč (Institute of Experimental Physics, Slovak Academy of Sciences)

123 Effect of Different Ratio of Eu$211$ Phase on the Superconducting Properties of EuBCO Bulk Superconductor

Bulk single crystals of EuBCO superconductors with different Eu$211$ phase contents were prepared. Higher growth rates in the growth temperature window than usual were used to grow bulk EuBCO crystals, and the Eu$211$ phase content in the samples was varied from $21.7$ to $32.2$ wt.$\%$.

Measurements of local superconducting properties (transition temperature, critical current density at $77$ K) and macroscopic superconducting properties (trapped magnetic field and levitation force at $77$ K) of the prepared materials were performed. The microstructure of the samples was studied by polarized light microscopy and scanning electron microscopy. The influence of different Eu$211$ phase contents, growth rates, resulting sizes and volume fraction distributions of Y$211$ particles on the measured superconducting properties was shown.

Acknowledgment

This work was supported by Slovak Grant Agency APVV-17-0625, APVV-21-0387, VEGA 2/0094/22. The work was created at the Institute of Experimental Physics of the SAS as part of the project solution SAS Return Project Scheme 2025.

Speaker: Dr Liudmila Vojtkova (Institute of Experimental Physics, Slovak Academy of Sciences)

124 Effect of Magnetic Field on Neutral Bath Containing Charged Brownian Particles

In the last two decades, the stochastic motion of charged particles in external magnetic fields has attracted considerable attention, mainly due to the necessity of taking into account memory effects in particle dynamics. The problem considered in this contribution is closely related to the Bohr-van Leeuwen theorem, which governs the response of equilibrium systems to external magnetic fields. Based on the Caldeira-Legget theory generalized to systems under the influence of a static magnetic field, we obtain equations of motion for the Brownian particles and oscillators constituting the bath in which the particle is embedded. The former equation is known as the generalized Langevin equation, which accounts for the frictional memory of the system. The Brownian particle is assumed to be charged while the bath particles are neutral. They thus do not respond to the external field but their interaction with the Brownian particle leads to changes in the bath state. Using the solution of the equations found, we calculate the average bath angular momentum and show that it persists for long times when the system is in equilibrium. This indicates a possible violation of the Bohr-van Leeuwen theorem for baths consisting of charged particles. However, this must be confirmed by a substantial generalization of the presented model when the bath particles feel the external field which affects memory in the dynamics of the system.

Acknowledgements

This work was supported by the grant VEGA 1/0353/22.

Speaker: Jana Tóthová (Technical University of Košice)

125 Effect of Uniaxial Single-Ion Anisotropy on Stability of Quantum and Thermal Entanglement in a Mixed-Spin Heisenberg Trimer

The effect of uniaxial single-ion anisotropy on quantum entanglement is rigorously quantified using negativity in a mixed spin-($1$,$1/2$,$1$) Heisenberg trimer accounting for different exchange coupling constants between identical and distinct spins. Bipartite negativities between the single spin entity and the remaining spin dimer are analyzed alongside with the global tripartite negativity of the whole trimer under the effect of an external magnetic field and the uniaxial single-ion anisotropy of easy-axis as well as easy-plane type. Interestingly, the uniaxial single-ion anisotropy significantly influences the degree of entanglement by altering the stability regions of energetically preferred ground states and it may also introduce additional phases in the overall ground-state phase diagram. Moreover, it is demonstrated that within specific ground states, the degree of entanglement basically depends on the strength of uniaxial single-ion anisotropy altering the respective probability amplitudes of the corresponding eigenvectors. Finally, the thermal stability of entanglement is discussed in detail including the emergence of a peculiar local minimum at finite temperatures. The obtained theoretical results may bring deeper insights into the bipartite and tripartite entanglement in trimetallic Ni$^{2+}$-Cu$^{2+}$-Ni$^{2+}$ molecular compounds.

Acknowledgements

This work was financially supported by the grant of the Slovak Research and Development Agency provided under the contract No. APVV-20-0150 and by the grant of The Slovak Academy of Science and The Ministry of Education, Science, Research, and Sport of the Slovak Republic provided under the contract No. VEGA 1/0695/23.

Speaker: Dr Hana Vargova (Institute of Experimental Physics, Slovak Academy of Sciences)

126 Effects of Single Crystal and Dipolar Anisotropy on Antiferromagnetic Order in the Frustrated fcc Magnet HoB$_{12}$

The rare earth boride HoB$_{12}$ crystallizes in the fcc structure and shows antiferromagntic order at $T_N = 7.4$ K. The ordering is described by an incommensurate ordering vector $Q_{af}$ = ($0.47,0.47,0.47$) [1]. In a magnetic field HoB$_{12}$ shows a complex phase diagram where nine different magnetic phases can be distinguished [2].

Here the phase diagram is discussed in the light of our recent determination of the single ion anisotropy using neutron scattering methods. The single ion anisotropy favors the alignment of the rare earth moment along the ($111$) directions. In the Ho-ion ground state we find an effective moment of $6$ $\mu_B$ in good agreement to magnetization data. Compared to the ordering temperature, excited crystal field states are much higher [3] and can be neglected here. The dipolar anisotropy is also relevant because the moment is quite large. We argue that the incommensurate ordering is caused by the dipolar interactions. A numerical spin wave calculation shows that the $0.5$ meV gap in the dispersion must also be caused by the dipolar interaction. The different phases observed in magnetic field result from the competition of the single crystal anisotropy and dynamic charge stripes [2]. It selects specific directions of the ordering vector without altering its absolute value. Selection rules will be given and compared to experimental data obtained from neutron diffraction.

Acknowledgements

This work was supported by projects DAAD-SAS-2023-02, APVV-23-0226, VEGA 2/0034/24.

References

[1] K. Siemensmeyer et al., “Magnetic Properties of the Frustrated fcc – Antiferromagnet HoB12 Above and Below T N,” Journal of Low Temperature Physics, vol. 146, no. 5–6. Springer Science and Business Media LLC, pp. 581–605, Jan. 25, 2007. https://doi.org/10.1007/s10909-006-9287-4
[2] K. Krasikov et al., “Suppression of indirect exchange and symmetry breaking in the antiferromagnetic metal HoB12 with dynamic charge stripes”, Physical Review B, vol. 102, no. 21. American Physical Society (APS), Dec. 28, 2020. https://doi.org/10.1103/physrevb.102.214435
[3] B. Z. Malkin et al., “Crystal-field potential and short-range order effects in inelastic neutron scattering, magnetization, and heat capacity of the cage-glass compound HoB12”, Physical Review B, vol. 104, no. 13. American Physical Society (APS), Oct. 29, 2021. https://doi.org/10.1103/physrevb.104.134436

Speaker: Dr Konrad Siemensmeyer (Helmholtz Zentrum Berlin)

127 Eu$_2$Pd$_3$Sn$_5$ - Structural and Physical Properties of a Novel Compound

In the Eu–Pd–Sn system some novel compounds have been discovered, showing a stable Eu$^{2+}$ magnetic state and complex magnetic structures, e.g. EuPdSn$_2$, Eu$_2$Pd$_2$Sn and EuPd$_2$Sn$_4$ [1–5]. The scenarios of complex and anisotropic magnetism are not expected for Eu$^{2+}$ because of its spin $S=7/2$ and orbital $L = 0$ numbers precluding the presence of crystal electric field effects. Following these studies, in this work we report on the first results of crystal structure and physical properties of the novel Eu$_2$Pd$_3$Sn$_5$ compound.

Eu$_2$Pd$_3$Sn$_5$ crystallizes in the orthorhombic $Ibam$ space group with lattice parameters $a = 11.079(3)$, $b = 12.900(4)$, $c = 6.4958(17)$ Å, being a new representative of the U$_2$Co$_3$Si$_5$ prototype. Atoms are distributed among 6 atomic sites, one ($8j$) occupied by Eu, two ($4b$, $8j$) by Pd and three ($4a$, $8g$, $8j$) by Sn species; the rare-earth Eu atoms are distributed as zigzag chains along both sides of the ($bc$) plane.

The temperature dependence of the $\chi$(T) magnetic susceptibility of Eu$_2$Pd$_3$Sn$_5$ measured in magnetic field $1$ T revealed a Curie-Weiss behavior down to $20$ K. The effective magnetic moment for Eu$_2$Pd$_3$Sn$_5$ is $\mu_{eff} = 7.85$ $\mu_B$ in good agreement with that of the free ion Eu$^{2+}$ value ($\mu_{eff} = 7.94$ $\mu_B$). The paramagnetic Curie temperature obtained from the fit is $\Theta_p = 8.72$ K, indicating the presence of ferromagnetic interaction in the sample. In $\chi(T)$ dependencies for low magnetic field $B = 0.01$ T two anomalies are present – antiferromagnetic-like at $13.8$ K and ferromagnetic-like at about $5$ K. The first one is completely absent with applying the magnetic field of $1$ T. Moreover, the $\chi(T)$ behavior for applied magnetic fields $B\geq 1$ T is typical of a ferromagnetic material. This scenario is supported with $C_p(T)$ specific heat measurements, where two anomalies ($\sim 13$ K and $5$ K) are present only for lower field $B \leq 1$ T. The $\lambda$-like anomaly at $\sim 13$ K is shifted in temperature with applying magnetic field and additionally the maximum becomes significantly broader. This behavior is usually found in ferromagnetic materials. Our results indicate a complex interplay between antiferromagnetism and ferromagnetism in novel Eu$_2$Pd$_3$Sn$_5$ compound.

Acknowledgements

This work was supported by the project VEGA 1/0511/24. Financial support from the Ministry of Higher Education and Scientific Research of Tunisia is also gratefully acknowledged

References

[1] I. Čurlík et al., “Crystal structure and physical properties of the two stannides EuPdSn2 and YbPdSn2,” Journal of Physics: Condensed Matter, vol. 30, no. 49. IOP Publishing, p. 495802, Nov. 15, 2018. https://doi.org/10.1088/1361-648x/aae7ae
[2] I. Čurlík et al., “The Magnetic Field Induced Ferromagnetism in EuPd2Sn4 Novel Compound,” physica status solidi (b), vol. 258, no. 6. Wiley, Apr. 15, 2021. https://doi.org/10.1002/pssb.202000633
[3] J.G. Sereni et al.,"Evidence for magnetic dimers and skyrmion lattice formation in Eu2⁢Pd2⁢Sn," Physical Review B, vol. 108, no. 1. American Physical Society (APS), Jul. 24, 2023. https://doi.org/10.1103/physrevb.108.014427
[4] A. Martinelli et al.,"Incommensurate magnetic cycloidal order in noncentrosymmetric E⁢u2⁢P⁢d2⁢Sn," Physical Review B, vol. 109, no. 10. American Physical Society (APS), Mar. 21, 2024. https://doi.org/10.1103/physrevb.109.104424
[5] A. Martinelli et al., “Magnetic phase separation in the EuPdSn2ground state,” Journal of Materials Chemistry C, vol. 11, no. 23. Royal Society of Chemistry (RSC), pp. 7641–7653, 2023. https://doi.org/10.1039/d3tc00764b

Speaker: Dr Ivan Čurlík (Faculty of Humanities and Natural Sciences, University of Prešov)

128 Experimental Study of Magnetostructure Correlations in Cu($tn$)(SCN)$_2$ System with Spin $S = 1/2$

Cu(tn)Cl$_2$ (tn = 1,3-diaminopropane) has been previously identified as a potential realization of a quasi-two-dimensional, spatially anisotropic triangular Heisenberg antiferromagnet with spin $1/2$, intralayer exchange coupling, $J/k_B \approx -3$ K, and interlayer exchange coupling, $J^{\prime} \approx 0.001\,J$. These studies indicated a field-induced anomaly forming below $1$ K in magnetic fields up to $7$ T and this anomaly was assigned to a Berezinskii-Kosterlitz-Thouless phase transition [1]. First-principle calculations point to the quasi-two-dimensional character of the exchange paths, while in the first approximation the system could be identified as a quasi-two-dimensional $S = 1/2$ Heisenberg antiferromagnet on the rectangular lattice with the intrachain coupling $J_1/k_B \approx$ $4.3$ K and the interaction ratio $R = J_2/J_1\approx$ $0.46$ [2].

In this work, we focused on the experimental study of magnetostructure correlations in Cu(tn)(SCN)$_2$ system with spin $S = 1/2$. Cu(tn)(SCN)$_2$ shows a similar chemical structure compared to Cu(tn)Cl$_2$ with the same system of hydrogen bonds [3]. Specific heat measurements of powder sample were performed in a commercial Physical Property Measurement System (PPMS) in the temperature range from $0.4$ K to $20$ K in magnetic fields up to $9$ T. The temperature dependence of susceptibility was measured in a commercial Quantum Design SQUID Magnetometer (MPMS) in the temperature range from $1.8$ to $300$ K in the magnetic field $100$ mT. The specific heat studies in zero magnetic field did not indicate a phase transition to long-range magnetic order down to $0.4$ K. The study of the susceptibility and magnetization of the Cu(tn)(SCN)$_2$ powder sample showed that the investigated system is characterized by an antiferromagnetic exchange interaction, which is approximately $10$ times smaller compared to the Cu(tn)Cl$_2$ system. The weakening of exchange interactions could be attributed to the presence of the isothiocyanato ligands.

Acknowledgements

The financial support of projects VEGA 1/0132/22, APVV-18-0197 and APVV-22-0172 is acknowledged.

References

[1] A. Orendáčová et al, “Interplay of frustration and magnetic field in the two-dimensional quantum antiferromagnet Cu($tn$)Cl$_2$,“ Physical Review B, vol. 80, no. 14. American Physical Society (APS), Oct. 21, 2009. https://doi.org/10.1103/physrevb.80.144418
[2] R. Tarasenko et al, “Extraordinary two-dimensionality in the $S=$ 1/2 spatially anisotropic triangular quantum magnet Cu(1,3-diaminopropane)Cl$_2$ with modulated structure,” Physical Review B, vol. 108, no. 21. American Physical Society (APS), Dec. 28, 2023. https://doi.org/10.1103/physrevb.108.214432
[3] A. O. Legendre et al., “A 2D coordination polymer with brick-wall network topology based on the [Cu(NCS)2(pn)] monomer,” Inorganic Chemistry Communications, vol. 10, no. 7. Elsevier BV, pp. 815–820, Jul. 2007. https://doi.org/10.1016/j.inoche.2007.04.005

Speaker: Dr Róbert Tarasenko (Institute of Physics, P. J. Šafárik University)

129 Exploring Altermagnetism in MnTe

One of the most characteristic features of altermagnets is their non-relativistic alternating spin-split band structures. Though these bands give rise to previously unexpected behavior in altermagnets of a certain symmetry, such as spin-polarized currents, it is the relativistic spin-orbit coupled bands that are the origin of many of the other T-reversal symmetry breaking phenomena of altermagnets, such as the anomalous Hall effect and X-ray magnetic circular dichroism. By combining both cutting-edge and well-established techniques, newly predicted properties of this class may be observed. Here I will present recent experimental developments and results highlighting the ability to not only measure some of these phenomena, but ways in which altermagnetic domains can be controlled and manipulated to aid in their detection.

References

[1] O. J. Amin et al., “Nanoscale imaging and control of altermagnetism in MnTe,” Nature, vol. 636, no. 8042, pp. 348–353, Dec. 2024, https://doi.org/10.1038/s41586-024-08234-x.
[2] A. Hariki et al., “X-Ray Magnetic Circular Dichroism in Altermagnetic $\alpha$-MnTe,” Phys. Rev. Lett., vol. 132, no. 17, Apr. 2024, https://doi.org/10.1103/physrevlett.132.176701.

Speaker: Alfred Dal Din (University of Nottingham)

130 Extraction of the Density of States and the Gap Function on a Temperature Smearing Scale From the Tunneling Conductance Data

The aim of our work is to extract the density of states (DOS) and the gap function from the tunneling conductance data at higher temperatures. It is known that if the temperature approaches zero, the DOS function is proportional to the tunneling conductance, and therefore, it can be easily extracted. However, with increasing temperature, the temperature smearing causes that this approximation can no longer be used. Thus, we have developed an algorithm that was designed to extract the details of the DOS function and the gap function on a typical temperature scale, which can be used approximately up to $1/2$ of $T_c$. Moreover, knowledge of the DOS in its normal state plays an important role. Hence, we present the results of the testing data sets and also the outcome from experimentally measured tunneling conductance data of the Nb$_3$Sn superconductor.

Acknowledgements

This work has been supported by the Slovak Research and Development Agency under the Contract no. APVV-23-0515, by the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie Grant Agreement No. 945478.

Speaker: Lucia Gelenekyová (Department of Experimental Physics, Faculty of Mathematics, Physics and Informatics, Comenius University)

131 Fast Cooling of the Hexanuclear Fe$^{3+}$ Cluster

Molecular magnets [1] with quantum correlations offer exciting possibilities for applications in demagnetization processes, as well as rapid cooling and heating [2]. This rapidly growing field presents diverse opportunities that leverage the unique properties of molecular magnets, bridging multiple scientific disciplines. In this work, we investigate the low-temperature thermodynamic properties of hexanuclear Fe$^{3+}$ complexes [3]. This complex exhibits competing interactions, $J_1$, $J_2$, and $J_3$, leading to $S = 1/2$ ground spin states within Fe$_3$O triangular subunits. These subunits are coupled via the $J_3$ interaction, giving rise to intricate quantum behavior.

We explore the magnetic Grüneisen parameter as a function of the magnetic field, revealing a pronounced magnetocaloric effect. During an adiabatic demagnetization process, a sharp cooling effect is observed near the transition field, where a ground-state phase transition occurs. Our findings highlight the potential of the hexanuclear Fe$^{3+}$ complex for fast quantum cooling and heating applications.

Acknowledgements

H. Arian Zad acknowledges the financial support provided under the postdoctoral fellowship program of P. J. Šafárik University in Košice, Slovakia. This work was supported by Slovak Research and Development Agency under the contract No. APVV-20-0150. M. Jaščur was partly supported by the grant of Ministry of Education, Science, Research and Sport of the Slovak Republic under Contract No. VEGA 1/0695/23.

References

[1] Kahn, O., Molecular Magnetism. New York, NY, USA: Wiley-VCH, 1993
[2] H. A. Zad et al., “Single-ion anisotropy effects on the demagnetization process of the alternating weak-rung interacting mixed spin-(1/2, 1) Ising-Heisenberg double saw-tooth ladders,” Physica Scripta, vol. 95, no. 9. IOP Publishing, p. 095702, Aug. 07, 2020. https://doi.org/10.1088/1402-4896/aba663
[3] J. Goura et al., “Synthesis, Structure, and Magnetic Properties of Phosphinate‐Bridged Hexanuclear FeIII Complexes Containing Two Butterfly‐Shaped Fe3O Cores,” European Journal of Inorganic Chemistry, vol. 2015, no. 34. Wiley, pp. 5601–5610, Nov. 03, 2015. https://doi.org/10.1002/ejic.201500890

Speaker: Hamid Arian Zad (Department of Theoretical Physics and Astrophysics, Faculty of Science, P. J. Sǎfárik University, Park Angelinum 9, 041 54 Košice, Slovak Republic)

132 Guided Exchange-Dipole Spin Wave in Monolayer CrSBr

CrSBr is an air-stable van der Waals antiferromagnet with high Néel temperature. We calculated the spin-wave spectrum for magnetization polarized along the three principal crystallographic axes of spin-wave wave guides based on a monolayer of CrSBr, which is the building block of bulk CrSBr, by considering the various magnetic interactions present in CrSBr, including the ferromagnetic exchange interaction, the triaxial anisotropy energy, the Zeeman interaction, and the magnetic dipolar interaction. Due to the symmetry of the considered interactions, the spin-wave state is characterized by definite parity under space inversion. In contrast to its short-range counterparts, the long-range dipolar field acts statically as a confining potential for the exchange-dipolar spin wave under investigation, while the dynamic dipolar interaction couples the spin and orbital motion of a magnon, thus giving rise to magnonic doublets with definite momentum. Effect of hybridization with acoustic phonons was investigated within the same framework. The numerical calculation tallies well with results obtained by micromagnetic simulation. Our study on the spin-wave eigenmode for a monolayer of CrSBr sheds light on the nature of exchange-dipole spin wave in a thin ferromagnetic slab; we confirm particularly that there is no topological protection for the Damon-Eshbach mode. Moreover, a thorough knowledge on the spin-wave eigenmode in monolayer CrSBr itself represents a step forward to understanding the more complicated antiferromagnetic resonance in bulk CrSBr.

Acknowledgements

This work was financially supported by Ministry of Education, Youth and Sports of the Czech Republic through project Quantum Materials for Applications in Sustainable Technologies (QM4ST) with the project number CZ.02.01.01/00/22_008/0004572.

Speaker: Daowei Wang (Department of Condensed Matter Physics, Charles University)

133 Hardness Anisotropy of HfC and TaC Ceramic Grains for Magnetic Applications

This study examines the nanoindentation behavior of polycrystalline hafnium carbide (HfC) and tantalum carbide (TaC) ceramics and validates the results through finite element (FE) simulation. The ceramics were synthesized via ball milling and a two-step Spark Plasma Sintering (SPS) process, producing uniform, single-phase samples. Electron backscatter diffraction (EBSD) was used to study orientation-dependent mechanical properties on the {001}, {101}, and {111} planes at room temperature.

HfC showed higher hardness on the {101} and {111} planes (~32 GPa) compared to {001} (~30 GPa), while TaC exhibited maximum hardness on the {111} plane (~23 GPa) and slightly lower values on {001} and {101} (~22 GPa). An axisymmetric FE model with a 70.3° conical indenter was used to simulate the indentation process. Simulated load-displacement curves aligned well with experimental data, supporting the observed trends. The orientation-dependent hardness variations were linked to active slip systems typical of rock-salt carbides. Minor discrepancies between simulation and experiment were negligible.

Hafnium carbide (HfC) and tantalum carbide (TaC) are ultra-high-temperature ceramics known for their exceptional thermal stability, hardness, and electrical conductivity. Although non-magnetic, they play a crucial role in magnetic applications under extreme conditions. In magnetic confinement fusion devices like tokamaks, they are used as plasma-facing materials due to their ability to endure intense thermal and particle flux without interfering with magnetic fields. Their chemical inertness and non-magnetic nature help maintain plasma stability and confinement. Recent studies have explored various ceramics for such applications [1,2]. Despite lacking magnetism, HfC and TaC are key to advancing magnetic technologies. This study specifically focuses on hardness, a fundamental characteristic necessary for withstanding extreme environment.

Acknowledgements

This research was supported by the Slovak Grant Agency for Science via the projects APVV-19-0497 and APVV-22-0493 and by the Slovak Academy of Sciences via the projects: Seal of Excellence - Strengthecs and IMPULZ IM-2022-67.

References

[1] A. Yehia, R. Vaßen, R. Duwe, and D. Stöver, “Ceramic SiC/B4C/TiC/C composites as plasma facing components for fusion reactors,” Journal of Nuclear Materials, vol.233-237, pp,1277-1270, 1996. https://doi.org/10.1016/S0022-3115(96)00155-9
[2] J. Linke, J. Du, T. Loewenhoff, G. Pintsuk, B. Spilker, I. Steudel and M. Wirtz, “Challenges for plasma-facing components in nuclear fusion,” Matter and Radiation at Extremes, vol. 4, no. 5, Art. no. 056201, Sep, 2019. https://doi.org/10.1063/1.5090100

Speaker: Yogesh Kumar Ravikumar (Institute of Materials Research, Slovak Academy of Sciences)

134 High-Entropy Cylindrite (FeSb$_2$Pb$_3$Sn$_4$)S$_{14}$ - Type Compounds: Mechanochemical Synthesis and Magnetic Properties

In recent years, multinary chalcogenides have received significant attention as potential energy materials. In their synthesis, mechanochemistry seems to be an effective method for the preparation of various chalcogenide - based nanoscale materials. Due to the creation of structural disorder, defects and nanostructuring in solids via high-energy milling, unique properties can be achieved [1]. Recently, a concept of high-entropy sulphides appeared for compounds created by combination of several elements [2]. For these systems stabilization effect, sluggish diffusion effect, severe lattice distortion effect and cocktail effect are characteristic [2]. Some of these effects are common also for mechanochemistry.

Based on advantages of mechanochemistry and high-entropy concept we investigated properties of (FeSbPbSnS) system subjected to high-energy milling applied during $15$-$2400$ min. The milling was performed in an intermittent regime and protective atmosphere. The synthesized samples were characterized using X-ray diffraction (XRD), nitrogen absorption, EDX-, TEM-, SAED, HRTEM- and HAADF- spectroscopy as well as by magnetic methods. XRD revealed prevailing presence of suredaite (PDF $01$-$070$-$3361$). Micrographs (TEM, SAED, HRTEM) revealed homogeneously aggregated grains with size less than $10$ to few tens of nanometers.

The magnetic nature of the synthesized samples was assessed from measurements in a direct current (DC) and an alternating current (AC) magnetic field. The isothermal magnetization curves measured at $5$ K and the field up to $5$ T reveal suppression of the iron ferromagnetism and the remarkable onset of the paramagnetic behavior with the increasing milling time. The paramagnetic nature is confirmed by the temperature-dependent magnetization curves. The spectra of the AC magnetic susceptibility measured in the frequency range from $1$ Hz to $250$ kHz show the well-relaxed behavior without any significant dispersion. The magnitude of the real part of the complex AC magnetic susceptibility decreases with the increasing milling time.

Acknowledgements

This work was supported by the projects of the Slovak Grant Agency VEGA (2/0112/22, 2/0029/24), and Slovak Research and Development Agency APVV 22-0115.

References

[1] P. Baláž, Mechanochemistry in Nanoscience and Minerals Engineering, Springer-Verlag, Berlin Heidelberg 2008. ISBN: 978-3-540-74854-0
[2] M. A. Buckingham et al., “High entropy metal chalcogenides: synthesis, properties, applications and future directions,” Chemical Communications, vol. 58, no. 58. Royal Society of Chemistry (RSC), pp. 8025–8037, 2022. https://doi.org/10.1039/d2cc01796b

Speaker: Dr Peter Baláž (Institute of Geotechnics, Slovak Academy of Sciences)

135 Influence of Hydrostatic and Uniaxial Pressure on the Anisotropic Quantum Magnet TmB$_4$

Application of external pressure, hydrostatic or uniaxial, is an appropriate way to change (tune) the properties of quantum magnets with geometrical frustration as it can modify the distances between atoms or layers, or change the angles in frustrated triangles [1-3]. In this contribution we present the influence of hydrostatic and uniaxial pressure on the magnetically strongly anisotropic thulium tetraboride (TmB$_4$), which is a metallic model system of the frustrated Shastry-Sutherland lattice (SSL), one of the most important and most studied models of quantum magnetism. In case of uniaxial pressures, three various orientations of pressure vs. crystal axes of the sample vs. magnetic field were set. In the first case pressure $p$ was applied parallel to the $c$ easy axis of magnetization and the magnetic field $H$ (i.e. $p \parallel [001] \parallel H$). In the second one was pressure applied in direction [110] and parallel to magnetic field ($p \parallel [110] \parallel H$). In the third orientation pressure was applied in direction [110], perpendicular to field $H$ and sample $c$ axis (i.e. $p \parallel [110] \perp (c \parallel H)$). The obtained results show that while hydrostatic pressure leads mainly to an increase of ordering temperature $T_N$, uniaxial pressure leads to a reduction of the strong magnetic anisotropy. This anisotropy reduction is apparently associated with the disturbance of crystal field effects and destruction of the frustrated SSL geometry in TmB$_4$.

Acknowledgements

This work was supported by projects APVV-23-0226, VEGA 2/0034/24, DAAD-SAS-2023-02. Liquid nitrogen for experiments was sponsored by U.S. Steel Košice, s.r.o.

References

[1] S. Haravifard et al., “Crystallization of spin superlattices with pressure and field in the layered magnet SrCu2(BO3)2,” Nature Communications, vol. 7, no. 1. Springer Science and Business Media LLC, Jun. 20, 2016. https://doi.org/10.1038/ncomms11956
[2] S. Bettler et al., “Sign switching of dimer correlations in SrCu2(BO3)2 under hydrostatic pressure,“ Physical Review Research, vol. 2, no. 1. American Physical Society (APS), Jan. 10, 2020. https://doi.org/10.1103/physrevresearch.2.012010
[3] Z. Shi et al., “Discovery of quantum phases in the Shastry-Sutherland compound SrCu2(BO3)2 under extreme conditions of field and pressure,” Nature Communications, vol. 13, no. 1. Springer Science and Business Media LLC, Apr. 28, 2022. https://doi.org/10.1038/s41467-022-30036-w

Speaker: Dr Slavomír Gabáni (Institute of Experimental Physics, Slovak Academy of Sciences)

136 Investigation of the Physical Properties of ZIF-$67$ and its Diamagnetic Counterpart ZIF-$8$

Zeolitic imidazolate frameworks (ZIFs) represent kind of porous metal−organic frameworks (MOFs) in which all tetrahedrally coordinated atoms are transition metals, and all bridging ones are imidazolate (Im) units. In Co(mIm)$_{2}$ (ZIF-$67$) and Zn(mIm)$_{2}$ (ZIF-$8$) where HmIm = $2$-methylimidazole (C$_{4}$H$_{6}$N$_2$), the structures are based on nets of linked CoN$_4$ or ZnN$_4$ tetrahedra, where mIm bridges make an M–mIm–M angle, close to $145$°, which is coincident with the Si–O–Si angle in zeolites. It was also found that Co-Zn substitution preserves the ZIF-8 structure up to $100\%$ Co(II) concentration, resulting in the formation of ZIF-$67$. ZIF-$8$/ZIF-$67$ hybrids exhibit improved catalytic and electrochemical energy storage capabilities [1].

In the present work the synthesis of both compounds in nanocrystalline form was performed. The obtained products were characterized through powder X-ray diffraction, infrared and Raman spectroscopy, confirming the identity of both materials which share an identical crystal structure and vibrational spectra, with the only distinction being the substitution of Zn by Co in ZIF-$67$. The heat capacity of powdered samples was experimentally studied within a temperature range of $0.4$ to $300$ K in zero magnetic field. While at higher temperatures the data coincide as a result of the same crystal structure, deviations appear at lower temperatures due to excitation of magnetic subsystem in ZIF-$67$. To isolate the magnetic contribution, lattice subtraction was performed using ZIF-$8$ in the $0.4$–$60$ K range, where the data sets could be distinguished. Additionally, the heat capacity of ZIF-$67$ was measured under various nonzero magnetic fields in the temperature interval from $0.4$ to $10$ K. It was observed that the heat capacity increases with the applied field; however, the field influence remains relatively weak. The calculated magnetic entropy in the temperature region between $0.4$ and $60$ K represents $95$ $\%$ of the theoretical maximum entropy for a spin-$3/2$ system. Moreover, the magnetic susceptibility of the nanocrystalline ZIF-$67$ sample was investigated between $2$ K and $300$ K under applied fields of $10$ mT and $1$ T in both field-cooled (FC) and zero-field-cooled (ZFC) conditions. A divergence between ZFC and FC curves was observed around $15$ K at $10$ mT, shifting to $5$ K at $0.1$ T and vanishing entirely at higher fields. The role of surface spins in magnetic properties is discussed.

Acknowledgements

The work was supported by the project APVV-22-0172, APVV-18-0197, VEGA 1/0132/22 and VVGS-2023-3040.

References

[1] S. Bakhtavar et al., “Three-dimensional porous g-C3N4 nanosheet, CNT and ZIF-8@ZIF-67-derived carbon nanoarchitecture composite as oxygen reduction electrocatalyst,” Materials Chemistry and Physics, vol. 328. Elsevier BV, p. 129993, Dec. 2024. https://doi.org/10.1016/j.matchemphys.2024.129993

Speaker: Liliia Kotvytska (Pavol Jozef Šafárik University in Košice, Faculty of Science, Institute of Physics)

137 Lanthanides MOFs Containing MTA$^{4-}$ in Magnetism

In recent years, lanthanide-based metal-organic frameworks (Ln-MOFs) have been gaining increasing attention due to their unique physicochemical properties and broad application potential. Ln-MOF materials are porous coordination polymers composed of lanthanide cations linked by organic ligands through coordination bonds [1]. Due to their partially filled $4f$ orbitals, lanthanides exhibit a strong tendency to form coordination polymers with high coordination numbers and diverse topologies, even when identical ligands are used. This structural flexibility enables the formation of extensive, highly organized networks with optimized properties for specific applications. Owing to the unique arrangement of electrons in $4f$ orbitals, Ln-MOF compounds find one of their key areas of application in magnetism [2].

In this work, we focused on the synthesis of new MOF materials prepared by coordinating the organic ligand H$_4$MTA with lanthanide ions. Solvothermal synthesis successfully yielded coordination polymers LnMTA (Ln = Nd(III), Sm(III), Eu(III)). The preparation of orange needle-shaped crystals of {[Ln$_4$(MTA)$_3$]$\cdot x$H$_2$O$\cdot y$DMF}$_n$ (LnMTA) was based on a hydrothermal reaction of Ln(NO$_3$)$_3\cdot 6$H$_2$O ($0.045$ mmol) with H$_4$MTA ($0.09$ mmol) in a DMF medium at $80$ °C for $6$ days. The synthesized coordination polymers were characterized using available physicochemical methods.The structure of the NdMTA complex was determined by single-crystal X-ray diffraction measurements. SC-XRD analysis revealed that the NdMTA complex crystallizes in an orthorhombic crystal system, where each MTA$^{4-}$ ion chelates four central neodymium atoms. The structure contains two types of cavities with dimensions of approximately $16.09\times 10.61$ Å$^2$ and $12.97\times 14.11$ Å$^2$ along the a-crystallographic axis. Based on PXRD analysis, it was confirmed that the prepared materials NdMTA, SmMTA and EuMTA are isostructural.The presence of the MTA$^{4-}$ ligand and solvent molecules within the cavities of the complex was confirmed by IR spectroscopy. Thermogravimetric analysis demonstrated that the porous complex undergoes desolvation upon heating to $150$ °C. The dehydrated form of LnMTA exhibits high thermal stability, maintaining its integrity up to $350$ °C. Magnetic properties were investigated using a SQUID based magnetometer in external dc field up to $5$ T and in the temperature range of $2 – 300$ K. Correlation between crystal structure of complexes and magnetic properties will be presented.

Acknowledgements

This work was supported by VEGA 1/0442/25 and APVV-20-0512. Funded by the EU NextGenerationEU through the Recovery and Resilience Plan for Slovakia under the project No. 09I03-03-V05-00008 (VVGS-ESGV-2923).

References

[1] W. Lu et al., “Tuning the structure and function of metal–organic frameworks via linker design,” Chem. Soc. Rev., vol. 43, no. 16. Royal Society of Chemistry (RSC), pp. 5561–5593, 2014. https://doi.org/10.1039/c4cs00003j
[2] S. Su et al., “Lanthanide Anionic Metal–Organic Frameworks Containing Semirigid Tetracarboxylate Ligands: Structure, Photoluminescence, and Magnetism,” Crystal Growth & Design, vol. 12, no. 4. American Chemical Society (ACS), pp. 1808–1815, Mar. 13, 2012. https://doi.org/10.1021/cg201283a

Speaker: Dr Nikolas Király (Pavol Jozef Šafárik University in Košice, Faculty of Science, Institute of Chemistry)

138 Lanthanum-Substituted Nickel-Zinc Ferrites Used as Fillers for Composites

Modern times and the associated rapid expansion of science and technology emphasize the need for new materials. This work deals with the analysis of the results of selected types of measurements, which can be used to determine the structural and magnetic properties of nickel-zinc ferrites with spinel structure. These are soft magnetic materials that have extensive use in various applications due to their suitable magnetic properties, high Curie temperature, high resistance, low dielectric losses and relatively cheap production. In various applications, it is necessary to use different parameters of ferrites, which can be achieved in several ways. One of the ways to change the magnetic properties ferrites, is a change in the proportions of the starting materials during the production of the sample. In our case, the ratio of nickel to zinc was the same for all the samples examined, namely $0.42 : 0.58$. Only the lanthanum content was changed. As a trivalent element, it belongs to the group of rare earths and, when entering the crystal lattice, occupies the positions of trivalent iron ions. Rare earths including lanthanum play an important role in influencing magnetic properties such as electrical resistance and power losses. They also play an important role in determining magnetocrystalline anisotropy. We varied the lanthanum content for values $x = 0, 0.02, 0.04, 0.06, 0.08$ and $0.1$, which appear in the formula Ni$_{0.48}$Zn$_{0.52}$La$_{x}$Fe$_{2-x}$O$_{4}$. The next options that affect the properties of ferrites are the methods of sample production, different firing temperatures and also the firing time. Our samples were produced by glycine-nitrate process based on auto-combustion preparation method and subsequently sintered at different temperatures ($T$ = $400$, $550$, $700$, $850$, $1000$, $1100$, $1200$, $1300$°C), all for $6$ hours. One sample was not sintered at all and is therefore a sample after decomposition. We evaluated the samples using a total of five methods. To determine the structural parameters, we used X-ray diffraction together with SEM micrographs. The magnetic properties of ferrites were measured using thermomagnetic analysis methods and hysteresis loop measurements. In addition, to analyze the use of the investigated ferrites as magnetic fillers in polymer composites, we used the results of measuring the frequency dependences of the complex permeability. The ferrite filler content in all investigated composites was $60$ vol.$\%$ percent and epoxy resin was used as the polymer matrix.

Acknowledgements

This work was supported by the Scientific Grant Agency of the Ministry of Education, Science, Research and Sport of the Slovak Republic (VEGA), under project no. 1/0041/24.

Speaker: Martin Šoka (Slovak University of Technology in Bratislava)

139 Localized Creation of Skyrmion Bubbles in Fe$_3$GaTe$_2$ by Conductive Atomic Force Microscopy

This study demonstrates the localized creation of skyrmions (SKs) in the two-dimensional ($2$D) ferromagnetic material Fe$_3$GaTe$_2$ using conductive atomic force microscopy (cAFM). By applying bias voltage through the cAFM tip, sufficient current is generated to induce localized Joule heating, transforming random stripe domains into bubble domains. SKs were successfully induced under ambient conditions and remained stable at room temperature, as confirmed by magnetic force microscopy (MFM). For Fe$_3$GaTe$_2$ layers with thicknesses of $1$ $\mu m$, $200$ nm, and $100$ nm, the average diameters of bubble domains were measured at $620\pm 100$ nm, $325 \pm 80$ nm, and $230 \pm 70$ nm, respectively, approximately $20\%$ larger than the pristine stripe width. By optimizing parameters such as bias voltage, application duration, and tip temperature based on Fe$_3$GaTe$_2$ thickness, the induced SK density could be precisely controlled, ranging from few SKs within areas $<5\mu m^{2}$ to nearly $10^4$ SKs within $1200$ $\mu m^{2}$. Furthermore, multi-point triggering demonstrated the re-writability of the domain structures, with non-overlapping domains remaining unaffected. These findings offer critical insights into the tunability of magnetic textures in $2$D ferromagnets, providing a foundation for developing next-generation spintronic devices based on $2$D heterostructures.

Speaker: Wen-Chin Lin (Department of Physics, National Taiwan Normal University)

140 Magnetic Field Induced Phase Transitions in Dimerized Quantum Magnets Cu(en)$_2$SO$_4$ and Cu(en)$_2$CrO$_4$

Previous single crystal studies of Cu(en)$_2$SO$_4$ (en = C$_2$H$_8$N$_2$) indicated the absence of phase transition to magnetic ordered state down to $0.3$ K [1]. Exponential decrease of specific heat at lowest temperatures indicated the presence of energy gap in the excitation spectrum. Detailed inspection of the crystal structure considering local symmetry of crystal field and spatial distribution of $d_{x^2-y^2}$ orbitals of Cu(II) ion expected formation of magnetic dimers within the $bc$ plane. The conjecture was confirmed by the analysis of thermodynamic data within the $S=1/2$ Heisenberg antiferromagnetic dimer model. As a manifestation of interdimer interactions, significant deviations from the simple dimer model appeared in the vicinity of the critical magnetic field $7$ T, associated with the gap closure. To tune the strength of magnetic dimerization, isomorphic compound Cu(en)$_2$CrO$_4$ was investigated in the present work. As a result of different molar masses, the scaling of lattice specific heat of Cu(en)$_2$SO$_4$ by a factor $1.08$ provides excellent agreement with Cu(en)$_2$CrO$_4$ data. Besides that, the analysis of thermodynamic data including specific heat, susceptibility and isothermal magnetization revealed reduction of the intradimer coupling from $5.5$ K in Cu(en)$_2$SO$_4$ to $4.5$ K in Cu(en)$_2$CrO$_4$. Corresponding critical field shifted from $7$ T to $5.5$ T and saturation field reduced from $11$ T (Cu(en)$_2$SO$_4$) to $8.5$ T. In both materials the magnetic phase diagrams are symmetric with a dome shape and the S-Cr substitution significantly shifted the induced ordered phase to lower magnetic fields and temperatures. To obtain better insight into the character of the magnetic subsystem in Cu(en)$_2$CrO$_4$, the first principle calculations of exchange interactions were performed. The studies confirmed expected distribution of magnetic dimers within the $bc$ plane and provided information about the distribution of interdimer couplings which are crucial for the setting of the ordered state. Considering the magnetic lattice within the $bc$ plane as predicted by first principle studies, quantum Monte Carlo simulations of thermodynamic properties were performed and the simulations were used for the analysis of experimental data.

Acknowledgements

The financial support of projects VEGA 1/0132/22, APVV-18-0197 and APVV-22-0172 is acknowledged. D.L. acknowledges project QM4ST no. CZ.02.01.01/00/22_008/0004572 from MEYS of the Czech Republic.

References

[1] O. Vinnik et al., “Magnetic field-induced phase transitions in Cu(en)2SO4 – A dimerized S = 1/2 quantum antiferromagnet,” Journal of Magnetism and Magnetic Materials, vol. 586. Elsevier BV, p. 171207, Nov. 2023. https://doi.org/10.1016/j.jmmm.2023.171207

Speaker: Dr Alžbeta Orendáčová (Šafárik University)

141 Magnetic Field-Assisted Electrodeposition of Ni$_3$Pt Mesoscopic Wires

Electrodeposition is an electrochemical technique used to synthesize nanostructured materials. By manipulating the experimental conditions (potential, current density, electrolyte composition, temperature, external magnetic field, etc.) it is possible to control the nucleation, growth, and assembly of the deposited material. This allows for fabrication of nanostructures with tailored dimensions, architectures and morphologies.

The application of an external magnetic field during electrodeposition introduces an additional degree of control over the process. The Lorentz force and Kelvin force, which act on the moving ions, within the electrolyte, can influence mass transport, convection, and even the nucleation and growth of the deposited structures.

Specifically, magnetic fields can alter the diffusion layer thickness, potentially enhancing or hindering ion transport to the electrode surface. Furthermore, magnetohydrodynamic effects can induce convective flows, which may impact the uniformity and morphology of the deposit.

In this work we investigated the effects of applying external magnetic field, during electrodeposition, on the magnetic properties of wires prepared from the Ni-Pt system. Samples with different geometries, including thin strips with various widths and a thin film, were prepared in varying orientations of the applied field. Their magnetic properties were measured via magnetic force microscopy and superconducting quantum interference device magnetometer. The results of these measurements were analyzed and compared to micromagnetic simulations.

Acknowledgements

Funded by the EU NextGenerationEU through the Recovery and Resilience Plan for Slovakia under the project No. 09I03-03-V05-00008 and the grant of the Slovak Research and Development Agency under the contract APVV-20-0324. S. Vorobiov acknowledges the financial support provided under the NextGenerationEU through the Recovery and Resilience Plan for Slovakia under project No. 09I03_03_V0400179.

Speaker: Branislav Stropkai (Pavol Jozef Šafárik University in Košice, Faculty of Science, Institute of Physics)

142 Magnetic Materials Formed With Additive Techniques

The use of additive techniques to shape polymer-bonded composites has become popular. Mixing the polymer with the metal powder makes it possible to obtain various new materials with different properties. One possible solution is to make composites based on magnetic powders in a low-density polyethylene (LDPE) matrix. Mixing process results in a bonded magnetic material with reduced magnetic properties compared to solid materials. However, the encapsulation of the powder in a polymer matrix allows it to be protected from environmental influences (oxidation). In addition, additive techniques make it possible to form magnetic cores of almost any shape without the need for sintering and electroplating.

The article is dedicated to discussing the process of manufacturing cores based on magnetic powders using additive manufacturing techniques ($3$D printing). The base magnetic powder was hot-mixed with LDPE. Once the homogeneous mass was obtained, the filament required for additive techniques was produced. Using a $3$D printer popular for FFF (Fused Filament Fabrication) techniques, core rings were made to measure the magnetic properties of this type of material. The magnetic properties of the manufactured cores were compared as a function of the percentage of base magnetic powder content. At the same time, the influence of the powder content on the manufacturing process by additive techniques was taken into consideration. The analysis carried out made it possible to identify the optimum parameters for the manufacturing process, including the optimum content of magnetic powder in the composite material.

Acknowledgements

This work was supported by the Warsaw University of Technology, Poland, through the Excellence Initiative Research University program, project number CPR-IDUB/227/Z01/2024.

Speaker: Krzysztof Siedlecki (Institute of Metrology and Biomedical Engineering, Warsaw University of Technology)

143 Magnetic Properties of Cu($en$)($sal$)Cl - A Quasi-Two-Dimensional $S=1/2$ Ferromagnet on a Square Lattice

Spin-$1/2$ copper (II)-based metal-organic compounds are known and extensively investigated examples of low-dimensional magnetic systems, where quantum fluctuations and particular coordination of the Cu$^{2+}$ ions determine their magnetic properties. In our study, we focused on an experimental study of system, Cu($en$)($sal$)Cl ($en=$ethylenediamine; $sal=$ salicylic acid). The structure hosts Cu$^{2+}$ ions within two uniquely distorted octahedral coordination environments: an axially elongated CuN$_4$Cl$_2$ unit formed by a pair of en ligands and a CuO$_4$Cl$_2$ unit formed by a pair of asymmetrically coordinated sal$^–$ anions. The crystal structure is unique because a chloride ion connects two copper (II) ions, creating a one-dimensional polymeric chain [1].

Specific heat measurements of powder sample were performed in a commercial Physical Property Measurement System (PPMS) in the temperature range from $0.4$ K to $30$ K in magnetic fields up to $9$ T. The temperature and magnetic field dependence of magnetization was measured in a commercial Quantum Design SQUID Magnetometer (MPMS) in the temperature range from $0.5$ to $300$ K in the magnetic fields up to $7$ T.

The specific heat studies in zero magnetic field indicated a phase transition to long-range magnetic order at $T_C = 0.82$ K, which was confirmed by the divergence ZFC and FC magnetization curves. It should be noted that at a temperature of $0.5$ K, a hysteresis loop was observed, indicating the presence of ferromagnetic interactions. Therefore, the experimental temperature dependence of the $\chi T$ product was analyzed using the $2$D Heisenberg ferromagnetic model, which is available in the form of the high-temperature series expansion (HTSE) relation provided for $S = 1/2$ [2]. The fit was performed in the temperature range $15–300$ K yielding $J/k_B\approx 2$ K and $g = 2.2$. On the other hand, the best agreement with specific heat data in zero magnetic field at temperatures above $1$ K was observed for the square lattice model with ferromagnetic intralayer coupling $J/k_B\approx 2$ K. The analysis of specific heat, magnetic susceptibility and magnetization identified the studied system as a quasi-two-dimensional $S = 1/2$ Heisenberg ferromagnet on the square lattice.

Acknowledgements

The financial support of projects VEGA 1/0132/22, APVV-18-0197 and APVV-22-0172 is acknowledged.

References

[1] S. S. Batool et al., “Crystal structure and spectroscopic characterization of a coordination polymer of Copper(II) chloride with ethylenediamine and the 2-hydroxybenzoate ion,” Journal of Structural Chemistry, vol. 57, no. 6. Pleiades Publishing Ltd, pp. 1176–1181, Nov. 2016. https://doi.org/10.1134/s0022476616060172
[2] G. A. Baker Jr. et al., “On the two-dimensional, spin- Heisenberg ferromagnetic models,” Physics Letters A, vol. 25, no. 3. Elsevier BV, pp. 207–209, Aug. 1967. https://doi.org/10.1016/0375-9601(67)90860-2

Speaker: Illia Kozin (Pavol Jozef Šafárik University in Košice, Faculty of Science, Institute of Physics)

144 Magnetic Properties of Heterometallic Ni$_{2}$M$_{2}$ (M = Mn, Co) Cubane Complexes

Magneto-structural correlations in a series of heterometallic isostructural cubane-type complexes with {Ni$_{2}$M$_{2}$($\mu_{3}$-O)$_{4}$} (M = Mn, Co) core: [Ni$_{2}$Mn$_{2}$(L)$_{2}$(OAc)$_{2}${N(CN)$_{2}$}]$\cdot 5$H$_{2}$O, [Ni$_{2}$Mn$_{2}$(L)$_{2}$(OAc)$_{2}$(N$_3$)$_{2}$]$\cdot$MeCN, [Ni$_{2}$Mn$_{2}$(L)$_{2}$(OAc)$_{2}$(NCS)$_{2}$]$\cdot$H$_{2}$O, and [Ni$_{2}$Co$_{2}$(L)$_{2}$(OAc)$_{2}$(NCS)$_{2}$]$\cdot 4$H$_{2}$O, were studied by magnetic studies, ab initio and Broken-Symmetry DFT calculations. This work marks the first-ever report of a Ni$_{2}$Mn$_{2}$ cubane structure, with only one prior structural example of a Ni$_{2}$Co$_{2}$ cubane complex. The estimated exchange interaction network in the cubane core is characterized by a competition between ferromagnetic (FM) and antiferromagnetic (AFM) exchange interactions. Specifically, the heterometallic exchange interaction mediated by the two $\mu_{3}$-O bridges is of AFM type, contrasting with FM exchange interaction when an additional $\mu$-O,O$^{\prime}$-acetate ligand is included in the exchange path. The Ni(II) centers exhibit octahedral coordination geometry yielding a moderate easy-plane anisotropy, while the Mn(II) and Co(II) ions adopt hepta-coordinated pentagonal bipyramidal geometries. The Ni$_{2}$Co$_{2}$ cubane features a rare example of hepta-coordinated Co(II) ions exhibiting easy-axis anisotropy with zero-field splitting parameter $D_{Co} \approx −23$ cm$^{–1}$. In addition, a field-induced slow magnetic relaxation was observed in Ni$_{2}$Co$_{2}$ cubane governed by a direct relaxation process.

Acknowledgements

Supported by CSIR, New Delhi, India (Sanction no. 01/3118/23/EMR-II), APVV-22-0172, APVV-23-0006, and National Competence Centre for High Performance Computing (project code: 311070AKF2, user project No. p696-24-2).

Speaker: Erik Čižmár (Institute of Physics, P.J. Šafárik University)

145 Magnetic Properties of Layered EuOCl and EuOBr Materials: Investigations and Mathematical Simulation

The Oxyhalides of rare earth elements (LnOHal; Ln- lanthanide; Hal = F; Cl; Br; are very interesting materials which find various applications as X-ray luminescent,screens, as anti-Stokes (frequency up shift) converters, commercial phosphors, displays and photosimulated materials.

Magnetic coupling between Ln$^{3+}$ ions is usually weak resulting in a Curie–Weiss type paramagnetic behaviour down to low temperatures. It is thus difficult to infer with certainty the nature or even the temperature of the magnetic ordering. The strong anisotropy of the rare earth oxyhalide structure may also be reflected in the magnetic properties.

The Ln$^{3+}$ ions have low-lying multiplets with high $J$-values and when these are split further by the strong crystal field of uniaxial C4v symmetry in LnOHal interesting magnetic phenomena might be observed.

The susceptibilities of EuOCl and EuOBr follow the paramagnetic Curie–Weiss behavior down to low temperatures. The temperature dependence of the experimental paramagnetic susceptibility for EuOCl and EuOBr was simulated with the aid of the van Vleck Formalism.

Speaker: Viktor Bunda (Department of Optics, Uzhgorod National University)

146 Magnetic Properties of the Dy$_{x}$Y$_{1-x}$(PO$_{3}$)$_{3}$ Glasses

The magnetic properties of rare-earth ions are mainly studied in the periodic and symmetrical crystal structures. The influence of the crystal-electric field (CEF), which surrounds the magnetic ions in such cases, is mainly identical for every magnetic ion.

We performed the experimental study of the magnetic properties of the Dy$_x$Y$_{1-x}$(PO$_3$)$_3$ glassy system with several concentrations of Dy$^{3+}$ ions, $x = 0$, $0.01$, $0.1$, $1$, $10$, and $100$ $\%$. The excess over the Debye contribution, called the boson peak, characterizes the specific heat $C_p$ of the non-magnetic sample ($x = 0$) at $T_{BP}\approx 12$ K [1], which is typical for the amorphous material. Additional magnetic contributions are observed in the magnetic samples ($x\neq 0$), revealed as an onset of Shottky maximum in the $x = 100$ sample [1]. The magnitude of the maximum decreases with the decreasing content of the magnetic ions. The external magnetic field application shifts the Shottky maximum to higher temperatures, which is connected with reducing the magnitude.

The magnetization measurements showed that saturated magnetization was lower than the expected saturation value $\mu_{eff} = 10.65\mu_B$ at $T= 1.8$ K due to the strong anisotropy of the Dy$^{3+}$ ions. Magnetic susceptibility measurements between $T=1.8$ K and $300$ K in the temperature range revealed no difference between zero field cooling and field cooling regimes, indicating the absence of magnetic phase transitions. The fitting procedure using Curie-Weiss law showed weak antiferromagnetic interactions, which decrease with lowering Dy$^{3+}$ concentrations. The effective magnetic moment at $T=300$ K indicates values close to $\mu_{eff} = 10.65\mu_B$.

AC susceptibility experimental study revealed the presence of slow magnetic relaxation in zero magnetic field characterized by the presence of one relaxation process. The relaxation process slows down with decreasing magnetic concentration. Sample with $x=100$ $\%$ relax above $f=10$ kHz, $x=10$ $\%$ at $f=3000$ Hz, $x=1$ % at $f=730$ Hz, $x=0.1$ $\%$ at $f=20$ Hz and $x=0.01$ $\%$ below $f=0.1$ Hz. This may be caused by the weakening of the magnetic interactions between Dy$^{3+}$ ions.

Acknowledgements

The work was supported by the project APVV-22-0172.

References

[1] P. Baloh et al., “Thermodynamic properties of the phosphate glass Dy(PO3)3 – Potential influence of boson peak on spin relaxation,” Journal of Magnetism and Magnetic Materials, vol. 588. Elsevier BV, p. 171415, Dec. 2023. https://doi.org/10.1016/j.jmmm.2023.171415

Speaker: Dr Vladimír Tkáč (Institute of Physics, Faculty of Science, P. J. Šafárik University in Košice)

147 Magnetic Tricriticality in Antiferromagnets

Applying a magnetic field to an antiferromagnet can cause abrupt changes to its magnetic state. A metamagnetic transition to a paramagnetic state is accomplished in sufficiently high magnetic fields. This transition is usually of a second-order type. However, a first-order transition is observed at low temperatures well below the Néel temperature in some cases. The antiferromagnet - paramagnet transition line in the field-temperature magnetic phase diagram having the first-order and second-order type segments is expected in Ising antiferromagnets with competing antiferromagnetic and ferromagnetic interactions. D. P. Landau has interpreted the point at which the two segments meet as a tricritical point [1]. Detailed experimental studies of tricriticality in antiferromagnets are rarely reported in the literature, although understanding these phenomena has fundamental importance. The field-induced state achieved by a first-order metamagnetic transition is often mistakenly considered ferromagnetic. However, it is a polarized paramagnetic state.

We have observed and studied in detail these intriguing phenomena in several diverse antiferromagnetic materials, such as a van der Waals insulator VBr$_3$ and intermetallic compounds UNiAl, UIrSi$_3$, CePtGe$_2$, UIrGe. We will discuss the results of the measurements of magnetization, specific heat, electrical, and Hall resistivity as functions of temperature and magnetic field characteristics for the first- and second-order magnetic phase transitions in these materials. Uniaxial crystal structures characterize the first three compounds, while the last two are orthorhombic. Nevertheless, all exhibit extreme magnetocrystalline anisotropy with one preferential magnetization axis, implying the Ising-like character of magnetism and spin-flip type metamagnetic transition. The source of considerable magnetocrystalline in VBr$_3$ is a significant orbital moment of the V$^{3+}$ ion. Theoretical calculations have confirmed the metamagnetic transition in this compound.

Unlike the first four colinear antiferromagnets, UIrGe exhibits a noncollinear magnetic structure but still displays characteristics of magnetic tricriticality. This aspect corroborates the idea that the appearance of the first-order type spin-flip metamagnetic transition at low temperatures results from the enormous magnetocrystalline anisotropy, which doesn’t allow continuous rotation of magnetic moments.

Acknowledgment

This work was supported by the Czech Grant Agency, project no. 25-15448S.

References

[1] D. P. Landau, “Magnetic Tricritical Points in Ising Antiferromagnets,” Physical Review Letters, vol. 28, no. 7. American Physical Society (APS), pp. 449–452, Feb. 14, 1972. https://doi.org/10.1103/physrevlett.28.449

Speaker: Prof. Vladimír Sechovský (Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University)

148 Magnetization Dynamics of Iron Garnet Thin Films and Heterostructures

Iron garnets, particularly yttrium iron garnet (YIG) and doped variants, are crucial materials for spintronic applications due to their exceptionally low damping ($\alpha \approx 10^{-5}$), high spin-wave propagation lengths, and tunable magnetic properties [1]. Understanding their magnetization dynamics in thin-film and heterostructure configurations is essential for advancing their integration into next-generation spintronic devices [2, 3].

In this study, we investigate the magnetization dynamics of Y$_3$Fe$_5$O$_{12}$ thin films and heterostructures using a combination of ferromagnetic resonance (FMR), magneto-optical Kerr effect (MOKE) microscopy, and Brillouin light scattering (BLS) spectroscopy. High-quality epitaxial iron garnet films were grown on lattice-matched substrates and characterized for structural and magnetic properties. FMR measurements were performed to extract key dynamical parameters, including Gilbert damping, in-plane anisotropy, inhomogeneous line broadening. The results reveal a strong dependence of damping and resonance field on film thickness, composition, and interface effects, particularly in heterostructures with Tm$_3$Fe$_5$O$_{12}$. MOKE microscopy enabled spatially resolved studies of magnetic domain and spin textures. BLS spectroscopy provided insights into spin-wave dispersion and lifetime, highlighting the interfacial induced Dzyaloshinskii-Moriya interaction (DMI) in asymmetric heterostructures.

Our findings offer a comprehensive understanding of the dynamic properties of iron garnet thin films and their heterostructures, paving the way for their optimized use in magnonics, nonvolatile memory, and spin-orbit torque-based devices.

Acknowledgements

We acknowledge the financial support from PATTERN (G. A. :No 101070506) and DEMURGE (Projet-ANR-22-CE30-0014).

References

[1] V. Cherepanov et al., “The saga of YIG: Spectra, thermodynamics, interaction and relaxation of magnons in a complex magnet,” Physics Reports, vol. 229, no. 3. Elsevier BV, pp. 81–144, Jul. 1993. https://doi.org/10.1016/0370-1573(93)90107-o
[2] Y. Fan et al., “Coherent magnon-induced domain-wall motion in a magnetic insulator channel,” Nature Nanotechnology, vol. 18, no. 9. Springer Science and Business Media LLC, pp. 1000–1004, Jun. 01, 2023. https://doi.org/10.1038/s41565-023-01406-2
[3] T. Fakhrul et al., “Damping and Interfacial Dzyaloshinskii–Moriya Interaction in Thulium Iron Garnet/Bismuth-Substituted Yttrium Iron Garnet Bilayers,” ACS Applied Materials & Interfaces, vol. 16, no. 2. American Chemical Society (ACS), pp. 2489–2496, Jan. 05, 2024. https://doi.org/10.1021/acsami.3c14706

Speaker: Imtiaz Bhatti (Laboratoire Albert Fert CNRS / Thales / Université Paris-Saclay)

149 Magneto-Raman and Magneto-Photoluminescence Spectroscopies on van der Waals Materials

Van der Waals (vdW) materials and their heterostructures exhibit remarkable electronic and optical properties that can be finely tuned using external physical fields such as photonic, magnetic, electric, and strain, or through proximity effects with other materials and molecules. These attributes position them as superior building blocks for cutting-edge optoelectronic and spintronic devices.

Raman (Ra) and photoluminescence (PL) micro-spectroscopies stand out as pivotal tools for delving into the electronic, optical, and spin phenomena within vdW and their heterostructures. Leveraging light with intrinsic chirality, these spectroscopic techniques offer a window into spin and valley-driven physics across diverse $2$DMs. Of particular significance, Ra and PL spectroscopies facilitate the exploration of magnetic order and quantum phenomena in van der Waals materials, owing to the robust spin-lattice coupling [1, 2]. Notably, recent advancements have unveiled the potential of the Ra/PL microscopy in elucidating magnetization reversal and magnetic domain mapping in various $2$D magnets and their heterostructures under applied magnetic fields. In this presentation, I will showcase selected findings from helicity-resolved cryomagnetic spectro-microscopies conducted on prominent $2$DMs, shedding light on their intriguing properties and potential applications.

Acknowledgements

The work was supported by the project AMULET, CZ.02.01.01/00/22_008/0004558.

References

[1] V. Varade et al., “Chiral Light Emission from a Hybrid Magnetic Molecule–Monolayer Transition Metal Dichalcogenide Heterostructure,” ACS Nano, vol. 17, no. 3. American Chemical Society (ACS), pp. 2170–2181, Jan. 18, 2023. https://doi.org/10.1021/acsnano.2c08320
[2] A. Ghosh et al., “Exotic magnetic and electronic properties of layered CrI3 single crystals under high pressure,” Physical Review B, vol. 105, no. 8. American Physical Society (APS), Feb. 08, 2022. https://doi.org/10.1103/physrevb.105.l081104

Speaker: Prof. Jana Kalbáčová Vejpravová (Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University)

150 Magnons in Altermagnets: Group-Theoretical Aspects

Altermagnets attract ongoing interest because of their unexpected electronic properties, such as spin splitting of electron bands or various transport properties (anomalous and spin Hall effects). Besides the electronic properties, based on elementary excitations that can be classified using the electron spin as a good quantum number, attention has recently been paid to magnons, where such simple classification is not possible. Nevertheless, magnon-related properties of altermagnets are interesting as well, including the chirality-based splitting of magnon eigenvalues [1] or various transport phenomena induced by temperature gradients [2, 3]. However, systematic classification of these magnon-related properties based on the group theory is not available at present.

In this contribution, magnons in a simple model of altermagnetism, corresponding to a two-dimensional bilayer, are studied within the classical isotropic Heisenberg Hamiltonian. Particular attention is paid to the splitting of magnon eigenvalues as well as to the spin currents generated by temperature gradients. The techniques used include the Bogoliubov transformation, the adiabatic linear-response theory, and the Shubnikov magnetic groups [4]. The obtained results are compared with those related to electronic excitations, namely, with the spin splitting of electron eigenvalues and with the spin currents generated by external electric fields. It is found that the previously developed classification scheme [4] is relevant for both electron-based and magnon-based properties.

Acknowledgements

The work was supported financially by the Czech Science Foundation (grant No. 23-04746S).

References

[1] L. Smejkal, et al., "Chiral magnons in altermagnetic RuO2," Physical Review Letters, vol. 131, no. 25. American Physical Society (APS), Dec. 20, 2023. https://doi.org/10.1103/physrevlett.131.256703
[2] M. Weißenhofer and A. Marmodoro, “Atomistic spin dynamics simulations of magnonic spin Seebeck and spin Nernst effects in altermagnets,” Physical Review B, vol. 110, no. 9. American Physical Society (APS), Sep. 19, 2024. https://doi.org/10.1103/physrevb.110.094427
[3] R. Hoyer et al., “Spontaneous crystal thermal Hall effect in insulating altermagnets,” Physical Review B, vol. 111, no. 2. American Physical Society (APS), Jan. 28, 2025. https://doi.org/10.1103/physrevb.111.l020412
[4] I. Turek, “Altermagnetism and magnetic groups with pseudoscalar electron spin,” Physical Review B, vol. 106, no. 9. American Physical Society (APS), Sep. 27, 2022. https://doi.org/10.1103/physrevb.106.094432

Speaker: Ilja Turek (Institute of Physics of Materials, CAS, Brno, Czech Republic)

151 Manifestations of Bound Magnons and Cluster-Based Haldane States in Magnetic Behavior of a Spin-1 Heisenberg Diamond Chain

We investigate the antiferromagnetic spin-1 Heisenberg diamond chain [1] in an external magnetic field using a combination of analytical and numerical techniques, including the theory of localized magnons, variational methods, exact diagonalization, and the density matrix renormalization group (DMRG). Our primary focus lies in understanding the magnetization process and magnetocaloric response at low temperatures, especially within a highly frustrated region of the parameter space. In this regime, we identify a rich variety of field-induced quantum phases, including uniform and cluster-based Haldane phases, monomer–dimer and bound-magnon crystal phases formed by one- and two-magnon bound states. These phases give rise to exotic features in the magnetization curve such as quantized magnetization plateaus and jumps, which are accurately captured using the localized magnon framework [2].

The magnetocaloric effect (MCE) is systematically analyzed under adiabatic conditions. We observe a pronounced MCE enhancement in the vicinity of magnetization plateaus and critical fields, particularly in the highly frustrated regime where the aforementioned quantum phases emerge. This phenomenon is especially significant in the context of low-temperature magnetic heating or refrigeration. The enhanced MCE in such systems enables substantial temperature changes under adiabatic conditions, making them promising candidates for cooling and heating applications in technological settings [3]. Furthermore, the magnetic Grüneisen parameter reveals thermodynamic signatures of field-tuned quantum phase transitions, providing deeper insight into the role of frustration and bound-magnon states in determining the system's thermal response. The particular attention is also focused on the cooling and heating capabilities of the spin-1 Heisenberg diamond chain. Our results highlight the utility of localized magnon theory in capturing both the magnetic and magnetocaloric signatures of frustration-driven quantum phases in low-dimensional spin systems.

Acknowledgements

This work was supported by Slovak Research and Development Agency under the contract No. APVV-20-0299 and under the contract No. VVGS-2023-2888, and by the grant of The Ministry of Education, Research, Development and Youth of the Slovak Republic under the contract No. VEGA 1/0298/25. H.A.Z. also acknowledges the financial support provided under the postdoctoral fellowship program of P. J. Šafárik University in Košice, Slovakia.

References

[1] K. Hida and K. Takano, “Ground-State Phase Diagram of S=1 Diamond Chains,” J. Phys. Soc. Jpn., vol. 86, no. 3, p. 033707, Mar. 2017, https://doi.org/10.7566/jpsj.86.033707
[2] J. Strečka, T. Verkholyak, J. Richter, K. Karl’ová, O. Derzhko, and J. Schnack, “Frustrated magnetism of spin-1/2 Heisenberg diamond and octahedral chains as a statistical mechanical monomer-dimer problem,” Phys. Rev. B, vol. 105, no. 6, Feb. 2022, https://doi.org/10.1103/PhysRevB.105.064420
[3] Honecker and Wessel, “Magnetocaloric effect in quantum spin-s chains,” Condens. Matter Phys., vol. 12, no. 3, pp. 399–410, 2009, https://doi.org/10.5488/cmp.12.3.399

Speaker: Azam Zoshki (Pavol Jozef Šafárik University in Košice, Faculty of Science, Institute of Physics)

152 Memory Effects of a Static Magnetic Field on Brownian Motion and the Absence of Classical Magnetism

The Bohr-van Leeuwen theorem stating the absence of classical magnetization in equilibrium, a fundamental result in the field of magnetic phenomena, was originally proved for an electron gas. In the present contribution, we raise the question of whether this theorem applies to systems of particles undergoing a non-Markovian Brownian motion among other particles in a static magnetic field. We consider charged Brownian particles immersed in a bath of neutral particles. The Brownian particles interact with the surrounding particles, which are mutually independent. The basic theory that we are coming from is the famous Caldeira-Legget model for bath oscillators. Generalizing this model to the presence of an external magnetic field, we derive the equations of motion for the oscillators and the Brownian particle. The latter equation has the form of a generalized Langevin equation that accounts for memory effects in the dynamics of the system. We show a way to obtain exact analytical solutions for the particles’ displacements and time correlation functions such as the mean square displacement. Using these solutions for the Ornstein-Uhlenbeck thermal noise, we show that at long times, when the system reaches equilibrium, the magnetic moment of the Brownian particles vanishes in accordance with the Bohr-van Leeuwen theorem.

Acknowledgements

This work was supported by the grant VEGA 1/0353/22.

Speaker: Prof. Vladimír Lisý (Technical University of Košice, Slovakia)

153 Polarization-Resolved Position-Sensitive CrSBr Photodetector

Polarization-sensitive photodetectors have attracted increasing research interest due to many important applications like high-density optical signal processing, imaging, navigation, or high-contrast polarizers. Here we demonstrate a self-powered photodetector with the assistance of the lateral photovoltaic effect resulting from the formation of Schottky junctions in the semiconducting CrSBr and Au electrode interfaces. We have investigated the polarization-resolved and self-powered device performance under the excitation of laser wavelength $514$ nm. We also demonstrated a strongly position-sensitive photoresponse in the device. The observed highly polarization-sensitive response of the device originated from the polarization-sensitive light–matter interaction in CrSBr was confirmed by measuring polarization-dependent photocurrent, Raman spectra, and photoluminescence (PL). Our work provides a viable route to fabricate air-stable, self-powered, high-performance polarization-sensitive photodetectors based on 2D layered materials.

Speaker: Martin Kalbac (J. Heyrovský Institute of Physical Chemistry)

154 Probing Dynamical Correlations, Structure Factors, and Entanglement in a Spin-$1/2$ Heisenberg Tetrahedron

This study rigorously investigates the effects of temperature and magnetic field on the dynamical autocorrelations and correlation functions of the spin-$1/2$ Heisenberg tetrahedron. The exact results for the dynamical autocorrelations and correlation functions are subsequently used to compute the static and dynamic structure factors of the spin-$1/2$ Heisenberg tetrahedron, which can be directly probed through inelastic neutron scattering experiments. It is demonstrated that experimental data on dynamic and static structure factors supplemented by basic magnetometry measurement of the magnetization enable the determination of fundamental bipartite entanglement measures of the spin-$1/2$ Heisenberg tetrahedron such as concurrence or negativity. Notably, anomalous temperature-induced variations in the structure factors and both investigated measures of the bipartite entanglement emerge in the vicinity of two magnetic fields, where level crossing between singlet-triplet and triplet-quintet ground states occur. Furthermore, the validity of our results is confirmed by verifying compliance with sum rules for the dynamic structure factor applicable at both zero as well as non-zero temperatures, which effectively ensures the conservation of spectral weight.

Acknowledgements

Funded by the EU NextGenerationEU through the Recovery and Resilience Plan for Slovakia under the project No. 09I03-03-V02-00021.

Speaker: Elham Shahhosseini Shahrabadi (Pavol Jozef Šafárik University in Košice, Faculty of Science, Institute of Physics)

155 Quantum Heisenberg Isotropic Ferromagnet With a Magnetoelastic Interaction

The total energy of real magnetic materials always includes, in addition to magnetic energy, the static lattice energy and the energy of thermal atomic vibrations. Despite this, most of the theoretical work on magnetic systems considers only the magnetic energy, completely ignoring lattice energy contributions. To clarify the influence of lattice energy on the magnetic properties of localized quantum spin systems, we assume that the total Helmholtz free energy includes the static lattice energy in the form of a volume-dependent Morse potential, the vibrational energy in the form of Grüneisen quasi-harmonic modification of Einstein phonon theory, and the magnetic contribution, represented by the quantum isotropic Heisenberg model with distance/volume-dependent nearest-neighbors exchange interactions. Using these basic inputs, we derived an analytical formula for the total energy, utilizing the methodology previously applied to Ising systems with magnetoelastic interactions [1]. Having obtained the Helmholtz free energy of the system, we calculated equations of state and all relevant thermodynamic quantities, using standard methods of statistical mechanics. Subsequently we performed extensive numerical calculations for a special case of a cubic lattice. Numerical results indicate that the region of stability of different magnetic phases varies significantly with the strengthening/weakening of the magnetoelastic coupling in the system. We discuss in detail the dependence of critical boundaries on freely adjustable model parameters and show that, in addition to second-order phase transitions, the isotropic Heisenberg model with strong magnetoelastic coupling also exhibits first-order phase transitions. This phenomenon is not observed in the traditional isotropic Heisenberg ferromagnet without magnetoelastic coupling. We support our conclusions by investigating the temperature dependences of magnetization, thermal expansion coefficients, and the Helmholtz free energy of the system.

Acknowledgements

Funded by the EU NextGenerationEU through the Recovery and Resilience Plan for Slovakia under the project No. 09I03-03-V02-00021, and by the Ministry of Education, Science, Research and Sport of the Slovak Republic under the project VEGA 1/0695/23.

References

[1] T. Balcerzak et al., “Self-consistent model of a solid for the description of lattice and magnetic properties,” Journal of Magnetism and Magnetic Materials, vol. 426. Elsevier BV, pp. 310–319, Mar. 2017. https://doi.org/10.1016/j.jmmm.2016.11.107

Speaker: Mr Majid Moradi (Pavol Jozef Šafárik University in Košice, Faculty of Science, Institute of Physics)

156 Scalable Effective Models for Complex Superconducting Nanodevices

Spin-$1/2$ molecules on superconductors represent a promising platform for advanced quantum devices. Recent experiments have shown that the ground-state phase and subgap states of molecular-superconductor hybrids, such as TBTAP [1] can be effectively tuned. A quantum phase transition can be induced by changing the distance between the STM tip and the molecule, or by adding another molecule and varying their mutual positions. These processes are faithfully described by the Superconducting Impurity Anderson Model (SCIAM) [2], which accommodates one or several impurities connected to one or multiple leads [3]. We investigate the phase diagrams and the evolution of subgap states for one, two, and three molecules coupled to the same lead. To achieve this goal, we have derived a Chain Expansion (ChE) method which maps superconducting leads into finite chains. We show that ChE-based effective models closely match the Numerical Renormalization Group (NRG) solutions of the full SCIAM across a broad parameter range, already for short chains solvable via Exact Diagonalization (ED). In more challenging regimes, the agreement between NRG and ChE calculations systematically improves with increasing chain length. The one-dimensional nature of ChE enables the usage of effective models with longer chain, inaccessible to ED, via the Density Matrix Renormalization Group. Interestingly, simpler systems, such as single quantum dot on a superconductor, require longer chains for converged ground-state expectation values in certain experimentally relevant regimes. Conversely, for more complex configurations, such as three coupled dots (trimers), shorter chains often suffice even there. Our findings demonstrate that ChE is a powerful tool for studying intricate superconducting systems, including those inaccessible to NRG, thus enabling investigations of superconducting structures relevant for quantum technologies and fundamental physics.

Acknowledgements

This work was supported by Grant No. 23-05263K of the Czech Science Foundation and by the Ministry of Education, Youth and Sports of the Czech Republic through the e-INFRA CZ (ID:90254).

References

[1] C. Li et al., “Individual Assembly of Radical Molecules on Superconductors: Demonstrating Quantum Spin Behavior and Bistable Charge Rearrangement,” ACS Nano, vol. 19, no. 3. American Chemical Society (ACS), pp. 3403–3413, Jan. 14, 2025. https://doi.org/10.1021/acsnano.4c12387
[2] V. Meden, “The Anderson–Josephson quantum dot—a theory perspective,” Journal of Physics: Condensed Matter, vol. 31, no. 16. IOP Publishing, p. 163001, Feb. 21, 2019. https://doi.org/10.1088/1361-648x/aafd6a
[3] P. Zalom et al., “Hidden Symmetry in Interacting-Quantum-Dot-Based Multiterminal Josephson Junctions,” Physical Review Letters, vol. 132, no. 12. American Physical Society (APS), Mar. 21, 2024. https://doi.org/10.1103/physrevlett.132.126505

Speaker: Daniel Bobok (Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic)

157 Spin-Crossover in Cu and Fe-Based Metallophthalocyanines: XAS and XMCD Investigations

Metallophthalocyanines (MPcs), planar aromatic macrocycles with transition metals such as Fe and Cu at their core, exhibit versatile electronic and magnetic properties, making them ideal candidates for applications in molecular spintronic, magnetic storage, and quantum computing  [1].

The previous magnetic study of CuPc and FePc grafted on high-density polyethylene (HDPE) was done using the EPR method  [2], where the components of the spectra are preserved in a wide temperature range confirming the assumption of very small zero-field splitting, however, the question of temperature-dependent spin-state has remained open. In this study, we investigate the surface electronic and magnetic properties of parent FePc and CuPc in bulk form, as well as FePc deposited on thin HDPE foil, using X-ray Absorption Spectroscopy (XAS) and X-ray Magnetic Circular Dichroism (XMCD) at temperature range $4$ K – $20$ K under varying magnetic fields ($2$ T – $6$ T). Our results reveal a strong XMCD signal evolution with temperature and magnetic field, providing insights into the spin states and ligand effects in both FePc and CuPc. The magnetic properties differ between bulk and foil materials, and a detailed analysis will be presented. For FePc deposited on HDPE foil, the XMCD measurements at $4$K show an increase in intensity with the applied magnetic field, and XAS and XMCD behaviour changes significantly with increasing of temperature up to $20$K at $2$T magnetic field, suggesting a possible field-induced spin crossover (HS $\rightarrow$ LS)  [3]. The differentiation between tetrahedral (Td) and octahedral (Oh) Fe sites is also analysed, highlighting the impact of local coordination on the magnetic response.

The application of XMCD sum rules allows us to extract the spin (ms) and orbital (ml) moments using the procedure described in  [4], further refining our understanding of the electronic structure and magnetic anisotropy in these systems.

References:

[1] M. Warner et al., “Potential for spin-based information processing in a thin-film molecular semiconductor,” Nature, vol. 503, no. 7477. Springer Science and Business Media LLC, pp. 504–508, Oct. 27, 2013. https://doi.org/10.1038/nature12597
[2] A. Reznickova et al., “Magnetic and Surface Properties of Metallophthalocyanines (M = Cu, Fe) Grafted Polyethylene,” The Journal of Physical Chemistry C, vol. 122, no. 2. American Chemical Society (ACS), pp. 1396–1403, Jan. 08, 2018. https://doi.org/10.1021/acs.jpcc.7b10984
[3] R. Pasquier and M. Alouani, “Calculated iron $L_{2,3}$ x-ray absorption and XMCD of spin-crossover Fe(phen)$_{2}$(NCS)$_{2}$ molecule adsorbed on Cu(001) surface,” 2023, arXiv. https://doi.org/10.48550/ARXIV.2309.02078
[4] P. V. B. Pinho et al., “Stoichiometry driven tuning of physical properties in epitaxial Fe3-Cr O4 thin films,” Applied Surface Science, vol. 615. Elsevier BV, p. 156354, Apr. 2023. https://doi.org/10.1016/j.apsusc.2023.156354

Speaker: Dr Mariia Holub (Synchrotron SOLEIL, L’Orme des Merisiers, BP48, 91192 Gif sur Yvette Cedex, France)

158 SQUID Magnetometry Applied to the Study of Surface Properties of Titanium Alloy Biomedical Implants

Titanium-based alloys have long been used for biomedical implants due to their biocompatibility, mechanical properties, and high corrosion resistance in body fluids. Moreover, their chemical composition and surface treatments can be tailored to enhance their performance. Electrochemical anodic oxidation (AO) is a promising method for improving implant integration with surrounding tissues and increasing their longevity [1].

In this study, we report the potential use of SQUID magnetometry for studying and screening the surface properties of Ti-$6$Al-$4$V alloy samples before and after AO treatment. The anodization was performed at voltages of $15$ V, $65$ V, and $90$ V using a $0.5\%$ wt. NaOH solution. Cylindrical samples ($\Phi$ $5\times5$ mm) were machined from Ti-$6$Al-$4$V alloys, grade ELI. Magnetic properties were measured using the Quantum Design MPMS XL-$7$T AC SQUID magnetometer.

The temperature dependence of mass magnetization, $M(T)$, was measured in zero-field cooling (ZFC) and field cooling (FC) modes at $50$ Oe. The DC magnetization, $M(H)$, was measured at $2$ K and $300$ K up to $20$ kOe. At room temperature, all samples exhibited nearly identical linear paramagnetic $M(H)$ curves. After correcting for the linear contribution of the sample holder and paramagnetism, nonlinear hysteresis loops were observed in the low-field range ($\pm5$ kOe), suggesting the presence of ferromagnetism, possibly due to structural defects in the surface oxide layer.

$M(T)$ dependencies in the temperature range of $300$ K to $30$ K showed a decrease with decreasing temperature, indicating antiferromagnetic ordering of magnetic moments. Below $5$ K, the $M(H)$ and $M(T)$ dependencies confirmed superconductivity with a critical temperature ($T_{C}^{ON}$) of approximately $5$ K. Additionally, the $M(T)$ dependencies were measured at $50$ kOe. A decrease of $T_{C}^{ON}$ to $\sim 3$ K can be observed, with the $M(T)$ value increasing by a factor of $103$ corresponding to the same magnetic field increase.

Significant differences in $M(H)$ dependencies were observed after correcting for the control samples (without AO) at $300$ K. These results suggest the potential use of SQUID magnetometry for studying and optimizing surface treatments of biomedical implants. Furthermore, we discuss certain aspects of the observed magnetic characteristics to better understand the existence of various exchange interactions.

Acknowledgements

This work was supported by the following projects: VEGA 2/0104/25, APVV-22-0328 and APVV-23-0366.

References

[1] A. Thakur and A. Kumar, “Recent advancements in the surface treatments for enhanced biocompatibility and corrosion resistance of titanium-based biomedical implants,” Applied Chemical Engineering, vol. 7, no. 1. Art and Science Press Pte. Ltd., Jan. 26, 2024. https://doi.org/10.24294/ace.v7i1.2042

Speaker: Andrej Dvurecenskij (Institute of Measurement Science, Slovak Academy of Sciences)

159 Structural and Magnetic Properties of a New Eu-Pd-Sn Compound: Eu$_3$Pd$_4$Sn$_{13}$

In our systematic exploration of the Eu-Pd-Sn ternary system, we have identified several new compounds, such as Eu$_2$Pd$_2$Sn, EuPd$_2$Sn$_4$, and EuPdSn$_2$. These Eu-based compounds often show a complex magnetic behavior. This behavior is unexpected since the intermetallics based on Eu$^{2+}$ (electron configuration 4f$^{7}$ and $^8$S$_{7/2}$ ground state) represent a pure spin system with $J=S=7/2$ and $L=0$ ($J$: total angular momentum; $S$: total spin angular momentum; $L$: total orbital angular momentum) which excludes crystal electric field effects. Consequently, these compounds are expected to exhibit negligible magnetic anisotropy although, on the contrary, they often show complex anisotropic magnetic ordering [1]. The interest in these compounds is due to the possible existence of topologically non-trivial magnetic textures that offer the potential for new magnetic information manipulation and storage technologies. For example, the magnetic structure of Eu$_{2}$Pd$_{2}$Sn shows significant analogies to the structure observed in EuNiGe$_{3}$ [2], possibly indicating the presence of a skyrmion lattice also for Eu$_{2}$Pd$_{2}$Sn [3].

In this work, we show the first results on a new compound synthesized in the Eu-Pd-Sn system, namely Eu$_{3}$Pd$_{4}$Sn$_{13}$. It crystallizes in the cubic Yb$_3$Rh$_4$Sn$_{13}$ structure type (space group P m -3 n) as confirmed by Rietveld refinement. The magnetic properties of this compound were investigated by measuring the magnetic susceptibility, the isothermal magnetization at different magnetic fields, and the specific heat. The trend of the inverse susceptibility as a function of temperature follows the Curie-Weiss plot with $\mu_{eff}=7.92$ $\mu_B$ in good agreement with the theoretical value of Eu$^{2+}$. Two effects were observed in the specific heat measurements, a very sharp effect at $6.5$ K pointing to a first-order transition, and a second at about 5 K. The magnetic susceptibility plot shows a magnetic kink at about $5$ K, which could indicate a complex interplay between antiferromagnetism and ferromagnetism.

Acknowledgements

Financial support from the Ministry of Higher Education and Scientific Research of Tunisia is gratefully acknowledged. This work was also supported by the project VEGA 1/0511/24.

References

[1] S. Seiro and C. Geibel, “Complex and strongly anisotropic magnetism in the pure spin system EuRh2Si2,” Journal of Physics: Condensed Matter, vol. 26, no. 4. IOP Publishing, p. 046002, Dec. 20, 2013. https://doi.org/10.1088/0953-8984/26/4/046002
[2] W. Iha et al., “Anomalous Hall Effect in Antiferromagnet EuNiGe3 with the Rashba-type Tetragonal Structure,” Proceedings of the International Conference on Strongly Correlated Electron Systems (SCES2019). Journal of the Physical Society of Japan, Mar. 18, 2020. https://doi.org/10.7566/jpscp.30.011092
[3] J. G. Sereni et al., "Evidence for magnetic dimers and skyrmion lattice formation in Eu2⁢Pd2⁢Sn," Physical Review B, vol. 108, no. 1. American Physical Society (APS), Jul. 24, 2023. https://doi.org/10.1103/physrevb.108.014427

Speaker: Ms Imen Trabelsi (Laboratory of Materials and Environment for Sustainable Development LR18ES10 & Department of Chemistry and Industrial Chemistry, University of Genova)

160 Study of Superconductivity in High-Entropy Alloy Films – Influence of Various Parameters

High-entropy alloys (HEAs) consist of several (typically $5$ or more) different types of randomly mixed constituent atoms displaying a high degree of disorder and thus high configurational entropy. Our recent research shown that main factors that influence their superconducting properties include crystal structure, valence electron count (VEC) and mixing entropy [1-3]. Thanks to possibility to prepare HEAs in form of films it is possible to prepare nitrides of such films within very wide range of N concentration. We have shown that with concentration of N the crystal structure can be changed from $bcc$ to $fcc$ and moreover VEC is modified. By appropriate combination of constituent atoms and by nitriding it is possible to tune VEC and mixing entropy in order to find relationship between them and superconducting properties of a given HEAs. Recent investigation of N incorporation into TiNbMoTaW high-entropy alloy (HEA) films has shown that in corresponding (TiNbMoTaW)$_{1.0}$N$_x$ nitrides this leads to a dome-like transition temperature $T_c$ vs concentration $x$ dependence with eightfold $T_c$ enhancement [2]. Here, we report about the impact of N incorporation into NbTaTiZrHf films that exhibit a lower configuration entropy and lower VEC than that of TiNbMoTaW. The obtained results show that the $T_c$ vs $x$ dependence in (NbTaTiZrHf)$_{1.0}$N$_x$ shows a significantly different course. In this contribution we will discuss influence of various parameters on superconductivity in HEAs.

Acknowledgements

This work was supported by projects Mobility Slovakia-Austria, AT-SK 2023-03-15-003, APVV-23-0624, and VEGA 2/0091/24. Liquid nitrogen for experiments was sponsored by U.S. Steel Košice, s.r.o. The thin film synthesis was supported by the Austrian Research Promotion Agency (FFG) under project number 871687.

References

[1] G. Pristáš et al., “Superconductivity in medium- and high-entropy alloy thin films: Impact of thickness and external pressure,” Physical Review B, vol. 107, no. 2. American Physical Society (APS), Jan. 17, 2023. https://doi.org/10.1103/physrevb.107.024505
[2] G. Pristáš et al., “Multiple transition temperature enhancement in superconducting TiNbMoTaW high entropy alloy films through tailored N incorporation,” Acta Materialia, vol. 262. Elsevier BV, p. 119428, Jan. 2024. https://doi.org/10.1016/j.actamat.2023.119428
[3] G. Pristáš et al., “Impact of annealing and hydrogenation on the superconducting transition temperature of (TiNbMoTaW)Nx high entropy alloy nitride films,” Solid State Sciences, vol. 161. Elsevier BV, p. 107851, Mar. 2025. https://doi.org/10.1016/j.solidstatesciences.2025.107851

Speaker: Dr Gabriel Pristáš (Institute of Experimental Physics, Slovak Academy of Sciences)

161 Superconducting Properties of GdBCO Bulk Superconductors Prepared by SDMG Process

GdBCO bulk superconductors possess unique superconducting properties, making them highly attractive for various practical applications [1]. They are typically prepared using the top-seeded melt growth (TSMG) process [2], in which a single-crystal seed is placed at the centre of the top surface of the pellet. Recently, a new method – single-direction melt growth (SDMG) – has been introduced [3]. In this approach, the single-grain bulk sample grows from a large seed on which the pressed pellet is placed, offering several advantages compared to TSMG-grown samples.

In this study, we prepared a GdBCO single-grain bulk superconductor with a nominal composition of $70$ wt$\%$ GdBa$_2$Cu$_3$O$_x$ (Gd123) + $30$ wt$\%$ Gd$_2$BaCuO$_5$ (Gd211) + $10$ wt$\%$ Ag$_2$O + $0.945$ wt$\%$ BaCeO$_3$ using the SDMG process. Macroscopic superconducting properties, including the trapped magnetic field and levitation force, were measured at liquid nitrogen temperature ($77.3$ K). The critical transition temperature, $T_c$, transition width, $\Delta T_c$ and $J_c(B)$ dependencies at $77$ K and $40$ K were evaluated at different positions within the bulk sample. Additionally, a detailed microstructural analysis, focusing on the size and volume fraction of Gd$211$ particles, was conducted in relation to the measured superconducting properties. The benefits of the GdBCO bulk samples prepared using the SDMG process, in contrast to those produced by TSMG, are discussed.

Acknowledgements

This work was supported by the Slovak Grant Agency (APVV-17-0625, APVV-21-0387), VEGA (No. 2/0044/19, No. 2/0094/22), and the European Union NextGenerationEU through the Recovery and Resilience plan for Slovakia under project No. 09I03-03-V04-00303.

References

[1] J. H. Durrell et al., “Bulk superconductors: a roadmap to applications,” Superconductor Science and Technology, vol. 31, no. 10. IOP Publishing, p. 103501, Sep. 11, 2018. https://doi.org/10.1088/1361-6668/aad7ce
[2] D. K. Namburi et al., “THE PROCESSING AND PROPERTIES OF BULK (RE)BCO HIGH TEMPERATURE SUPERCONDUCTORS: CURRENT STATUS AND FUTURE PERSPECTIVES,” Superconductor Science and Technology. IOP Publishing, Jan. 21, 2021. https://doi.org/10.1088/1361-6668/abde88
[3] T. Motoki et al., “Development of homogeneous and high-performance REBCO bulks with various shapes by the single-direction melt growth (SDMG) method,” Superconductor Science and Technology, vol. 35, no. 9. IOP Publishing, p. 094003, Jul. 21, 2022. https://doi.org/10.1088/1361-6668/ac811e

Speaker: Dr Daniela Volochová (Institute of Experimental Physics, Slovak Academy of Sciences)

162 Superconductivity in (NbMoTaW)-C-N Carbonitride Films

Superconductivity in high and medium entropy alloys (HEAs and MEAs) have been the subject of considerable interest in the recent period (see e.g. [1 - 3]). Very recently, also the HEA nitrides and carbonitrides have attracted attention due to their transition temperature ($T_c$) enhancement [4] and observation of unconventional superconductivity [5].

In this work we present results of the research of the superconducting properties of reactive DC magnetron co-sputtered (NbMoTaW)-C-N films with a wide range of carbon and nitrogen concentration values. From observed concentration dependencies of $T_c$ it follows that the presence of carbon plays the main role in the observed (triple) $T_c$ enhancement. Based on the conventional phonon-mediated BCS theory of superconductivity this seems to be related to the lower atomic mass of C compared to that of N, and the parallel increase of the electron-phonon interaction due to the different bonding of carbon atoms (compared to nitrogen) to the HEA or MEA metallic sub-lattice.

Acknowledgements

This work was supported by the Slovak Academy of Sciences by the EU NextGenerationEU through the Recovery and Resilience Plan for Slovakia under project No. 09I03-03-V04-00281, by the Slovak Research and Development Agency (project APVV 21-0042) and VEGA 2/0091/24.

References

[1] L. Sun and R. J. Cava, “High-entropy alloy superconductors: Status, opportunities, and challenges,” Physical Review Materials, vol. 3, no. 9. American Physical Society (APS), Sep. 03, 2019. https://doi.org/10.1103/physrevmaterials.3.090301
[2] J. Kitagawa et al., “Cutting Edge of High-Entropy Alloy Superconductors from the Perspective of Materials Research,” Metals, vol. 10, no. 8. MDPI AG, p. 1078, Aug. 10, 2020. https://doi.org/10.3390/met10081078
[3] G. Pristáš et al., “Superconductivity in medium- and high-entropy alloy thin films: Impact of thickness and external pressure,” Physical Review B, vol. 107, no. 2. American Physical Society (APS), Jan. 17, 2023. https://doi.org/10.1103/physrevb.107.024505
[4] G. Pristáš et al., “Multiple transition temperature enhancement in superconducting TiNbMoTaW high entropy alloy films through tailored N incorporation,” Acta Materialia, vol. 262. Elsevier BV, p. 119428, Jan. 2024. https://doi.org/10.1016/j.actamat.2023.119428
[5] L. Zeng et al., "Superconductivity and non-trivial band topology in high-entropy carbonitride Ti0.2Nb0.2Ta0.2Mo0.2W0.2C1-xNx," The Innovation Materials, vol. 1, no. 3. Innovation Press Co., Limited, p. 100042, 2023. https://doi.org/10.59717/j.xinn-mater.2023.100042

Speaker: Dr Karol Flachbart (Institute of Experimental Physics, Slovak Academy of Sciences)

163 The Role of Local Vibrational Modes in Magnetic Relaxation of [Gd(H$_2$O)$_6$Cl$_2$]Cl

Static and dynamic magnetic properties, electron-spin resonance spectra together with calculation of low-energy vibrational modes for complex [Gd(H$_2$O)$_6$Cl$_2$]Cl are presented. The studied compound can be identified as $S = 7/2$ Heisenberg magnet with easy-axis anisotropy $D/k_B \approx - 50$ mK and dipolar magnetic coupling of nominal size $\left| J/k_B \right| \approx 12$ mK. The existence of low-energy local vibrational modes possessing energies lower than $200$ cm$^{-1}$ was revealed by numerical simulations. The analysis of low-temperature lattice specific heat indirectly supported their existence. The presence of two relaxation channels was revealed by the investigation of slow magnetic relaxation induced by static external magnetic field $0.4$ T. For the first process, extremal slow relaxation in the time scale of seconds was attributed to the coexisting Raman and Orbach-like processes involving various energy levels from a multi-level system created by Gd$^{3+}$ ion doublets split in the external magnetic field. Temperature dependence of the relaxation time for the second process could be described by $\tau \approx T^{-2.18}$, which represents substantial deviation from $\tau \approx T^{-3}$ being anticipated to arise from the coexistence of standard Raman relaxation for a multilevel system $( \tau \approx T^{-5} )$ and the interaction of a magnetic ion with low-energy local vibrational modes $(\tau \approx \exp(\Delta_{loc}/T) )$ proposed for various single molecule magnets [1]. However, magnetic field dependence of the relaxation time was found to be consistent with resonant phonon trapping $(\tau \approx T^{-2})$ and the assumptions for the onset of the trapping in [Gd(H$_2$O)$_6$Cl$_2$]Cl were verified. The obtained results suggest that the low-energy local vibrational modes, despite being present in a system, may not introduce the governing relaxation mechanism.

Acknowledgements

This work was supported by Slovak research and development agency under contract APVV-22-0172, and partially by the EU NextGenerationEU through the Recovery and Resilience Plan for Slovakia under the project No. 09I03-03-V04-00176.

References

[1] L. Gu and R. Wu, “Origin of the anomalously low Raman exponents in single molecule magnets,” Physical Review B, vol. 103, no. 1. American Physical Society (APS), Jan. 04, 2021. https://doi.org/10.1103/physrevb.103.014401

Speaker: Hryhorii Titikov (Pavol Jozef Šafárik University in Košice, Faculty of Science, Institute of Physics)

164 Thermal Phase Transitions in a Deformable Quantum Spin–$1/2$ XX Chain in a Transverse Magnetic Field

Incorporating magnetoelastic coupling into one-dimensional spin models makes them more realistic and can introduce novel physical phenomena. We investigate the deformable quantum spin-$1/2$ XX chain in a transverse magnetic field, which is exactly solvable within a combination of Jordan-Wigner and Fourier transformations. Lattice deformations are introduced into this quantum spin-chain model by accounting for a magnetoelastic coupling that depends linearly on a lattice distortion [1]. The primary outcome of our calculations is the variational Gibbs free energy, which is minimized with respect to a small distortion parameter. Subsequently, we compute the magnetization and magnetic susceptibility as fundamental indicators of the magnetic properties. In addition, we have also examined in detail the respective behavior of elastic properties such as the equilibrium value of the distortion parameter and inverse compressibility. The rigid spin-$1/2$ XX chain exhibits a quantum phase transition driven by the transverse magnetic field. In the deformable spin-$1/2$ XX chain in the transverse magnetic field we contrarily uncover first-order transition line extending from zero to finite temperatures, which eventually terminates at a critical point associated with a continuous thermal phase transition. The thermal first-order phase transitions emerging at sufficiently low temperatures are accompanied with a magnetic hysteresis, which is gradually suppressed by increasing temperature.

Acknowledgements

This work was financially supported by The Ministry of Education, Research, Development and Youth of the Slovak Republic under the grant No. VEGA 1/0298/25, by the Slovak Research and Development Agency under Contract No. APVV-22-0172, and by the internal grant of Faculty of Science of Pavol Jozef Šafárik University in Košice under the contract No. VVGS-2025-3497.

References

[1] O. Derzhko et al., “Compressibility of deformable spin chains near quantum critical points,” The European Physical Journal B, vol. 86, no. 3. Springer Science and Business Media LLC, Mar. 2013. https://doi.org/10.1140/epjb/e2013-30979-4

Speaker: Dávid Sivý (Pavol Jozef Šafárik University in Košice, Faculty of Science, Institute of Physics)

165 Two-Gap Superconductivity in the Non-Centrosymmetric La$_{3}$Se$_{4}$ Compound

Non-centrosymmetric superconducting materials represent a class of materials with existing unconventional properties. Thanks to the broken inversion symmetry these materials can exhibit properties such as mixed-parity pairing and very high upper critical magnetic field. Point-Contact Andreev reflection spectroscopy can be a great technique for studying these phenomena. Point-contact spectroscopy measurements at low temperatures and high magnetic fields have been performed on a non-centrosymmetric La$_3$Se$_4$ superconductor with a critical temperature $T_{c} = 8$ K. Two superconducting energy gaps $\Delta_{1}$ and $\Delta_{2}$, with $2\Delta_{1}/k_{B}T_{c} \sim 5.8$ and $2\Delta_{2}/k_{B}T_{c} \sim 2.3$, are directly observed in some of the spectra. The temperature and magnetic field effects help to resolve a two-gap structure even on the most frequent spectra where at low temperatures only a single gap is apparent, reflected in a pair of maxima around the zero bias. The claim of two-gap superconductivity is also supported by the heat capacity and the Hall probe magnetization measurements.

Acknowledgements

This work was supported by the Slovak Research and Development Agency under Contract No. APVV-20-0425, by the Science Grant Agency project VEGA 2/0073/24, COST action No. CA21144 (SUPERQUMAP), Slovak Academy of Sciences Project No. IMPULZ IM-2021–42. The work in Dresden was supported by the German Research Foundation (DFG) within the Walter Benjamin research Grant No. NA 2012/1-1.

Speaker: Filip Košuth (Institute of Experimental Physics, Slovak Academy of Sciences)

166 Unveiling the Degeneracy of Bound-Magnon States from Magnetic and Magnetocaloric Properties of the Spin-$1/2$ Heisenberg Octahedral Chain

Magnetic, thermodynamic, and magnetocaloric properties of the spin-$1/2$ quantum Heisenberg octahedral chain with three distinct exchange interactions in an external magnetic field are investigated. The exact results derived for the one-magnon energy spectrum suggest the existence of three flat bands among five one-magnon energy bands, which allow the application of the theory of localized magnons for the description of low-temperature magnetic and magnetocaloric properties, independently verified through numerical exact diagonalization. One of the flat bands corresponds to a magnon bound to a single square plaquette, whereas the other two flat bands correspond to a two-fold degenerate dimer-singlet state residing on two opposite corners of the square plaquette. The case in which the next-nearest-neighbor interaction on the square plaquette is absent has been previously studied [1]. In this work, the influence of this interaction is analyzed in detail alongside the nearest-neighbor interaction on the square plaquette, leading to a more complete understanding of the system's properties. The magnetization process exhibits characteristic jumps near the saturation magnetic field, which result from a level crossing between the magnon-crystal eigenstate and fully polarized ferromagnetic state. The temperature-dependent interception point of magnetization curves is shown to be significantly influenced by the degree of degeneracy of the respective flat one-magnon state. A similar analysis is conducted for the heat capacity, which displays significant variations near phase transitions between different quantum ground states. Furthermore, the magnetocaloric effect is examined, with a particular focus on cooling via the adiabatic demagnetization process. The results indicate that the system facilitates efficient temperature reduction upon a gradual decrease of the external magnetic field, making it a promising candidate for magnetocaloric applications in cryogenic cooling.

Acknowledgements

This work was financially supported by The Ministry of Education, Research, Development and Youth of the Slovak Republic under the grant No. VEGA 1/0298/25, by the Slovak Research and Development Agency under Contract No. APVV-20-0150, and by the internal grant of Faculty of Science of Pavol Jozef Šafárik University in Košice under the contract No. VVGS-2025-3497.

References

[1] J. Strečka et al., “Spectacular diversity of quantum ground states and quantum phase transitions of a spin-1/2 Heisenberg octahedral chain”, Physical Review B, vol. 95, no. 22. American Physical Society (APS), Jun. 13, 2017. https://doi.org/10.1103/physrevb.95.224415

Speaker: Michal Nemcik (Pavol Jozef Šafárik University in Košice, Faculty of Science, Institute of Physics)

167 Upper Critical Fields Obtained Within Different Approaches for Optimally-Doped YBa$_2$Cu$_3$O$_{7-\delta}$ Thin Films

The development of a comprehensive theory capable of fully describing high-temperature superconductors (HTSCs) remains one of the most challenging problems in modern solid-state physics. HTSCs with a superconducting (SC) transition temperature $T_c$ exceeding the boiling point of liquid nitrogen include a well-known class of metal oxides with an active CuO$_{2}$ plane such as YBa$_2$Cu$_3$O$_{7-\delta}$ (or YBCO), commonly referred to as cuprates. These type-II superconductors exhibit a strong $d$-wave anisotropy, low charge carriers density, strong electronic correlations, and quasi-two-dimensionality, as established by numerous studies [1-4].

The high $T_c$-values result in a short size of Cooper pairs, determined by the coherence length. In a crystal lattice, the coherence lengths differ significantly depending on direction: the in-plane coherence length $\xi_{ab}$ is an order of magnitude greater than the out-of-plane coherence length $\xi_{c}$. To determine $\xi_{ab}(T)$ and $\xi_{c}(T)$, it is necessary to measure the temperature dependence of the upper critical field $H_{c_2}(T)$ for magnetic fields applied parallel to both the $ab$-plane and the $c$-axis.

The work provides information about a comparison of the upper critical fields $H_{c_2}(T)$ for optimally doped YBa$_2$Cu$_3$O$_{7-\delta}$ thin films, calculated using Ginzburg-Landau (GL) and Werthamer-Helfand-Hohenberg (WHH) theories. For different magnetic field orientations, WHH theory yields $\mu$$_{0}$$H_{c_2}(0)$ values of $638$ T for $H \parallel ab$ and $153$ T for $H \parallel c$. The GL theory predicts significantly overestimated values, providing, however, a better fit to experimental data.

References

[1] R. Haussmann, “Properties of a Fermi liquid at the superfluid transition in the crossover region between BCS superconductivity and Bose-Einstein condensation,” Physical Review B, vol. 49, no. 18. American Physical Society (APS), pp. 12975–12983, May 01, 1994. https://doi.org/10.1103/physrevb.49.12975
[2] V. M. Loktev et al., “Phase fluctuations and pseudogap phenomena,” Physics Reports, vol. 349, no. 1. Elsevier BV, pp. 1–123, Jul. 2001. https://doi.org/10.1016/s0370-1573(00)00114-9
[3] O. Tchernyshyov, “Noninteracting Cooper pairs inside a pseudogap,” Physical Review B, vol. 56, no. 6. American Physical Society (APS), pp. 3372–3380, Aug. 01, 1997. https://doi.org/10.1103/physrevb.56.3372
[4] J. R. Engelbrecht et al., “Pseudogap above $T_c$ in a model with $d_{x^2-y^2}$ pairing,” Physical Review B, vol. 57, no. 21. American Physical Society (APS), pp. 13406–13409, Jun. 01, 1998. https://doi.org/10.1103/physrevb.57.13406

Speaker: Yevhen Petrenko (Institute of Experimental Physics, Slovak Academy of Sciences)

168 Weak Ferromagnetism in Two-Dimensional Transition Metal Tetrafluoride Altermagnets

Altermagnets are a recently identified class of magnetic materials that, like antiferromagnets, exhibit zero net magnetization but display spin-split electronic bands in certain regions of the Brillouin zone [1]. Unlike conventional antiferromagnets, altermagnets can support spin-polarized currents, making them a unique hybrid between antiferromagnets and ferromagnets. This duality provides several advantages for spintronic applications, including spin currents without stray fields, robustness against external magnetic fields, ultrafast spin dynamics, and symmetry-driven spin phenomena.

Two-dimensional ($2$D) altermagnetic materials are particularly compelling. Not only were they initially predicted theoretically, but in the presence of spin-orbit coupling (SOC), some exhibit weak ferromagnetism due to non-trivial spin-momentum locking that cants their magnetic moments [2].

In this poster, we present a combined density functional theory and symmetry analysis of the electronic structure of $2$D transition metal tetrafluorides. We examine how the net magnetic moment scales with SOC strength and use group theory to derive an effective spin Hamiltonian that captures both the spin splitting and spin-momentum locking of the bands. By disentangling altermagnetic contributions from those induced by SOC, we clarify the role of spin-orbit interaction in modifying the intrinsic altermagnetic behavior. Our results highlight the emergence of weak ferromagnetism and non-trivial spin textures in $2$D altermagnets, pointing toward new directions in the design of next-generation spintronic materials.

Acknowledgements

This work was supported by the Slovak Research and Development Agency under the Contract no. SK-SRB-23-0033, and by the Ministry of Education, Research, Development and Youth of the Slovak Republic provided under Grant No. VEGA 1/0104/25.

References

[1] L. Šmejkal et al., “Emerging Research Landscape of Altermagnetism,” Physical Review X, vol. 12, no. 4. American Physical Society (APS), Dec. 08, 2022. https://doi.org/10.1103/physrevx.12.040501
[2] M. Milivojević et al., “Interplay of altermagnetism and weak ferromagnetism in two-dimensional RuF4,” 2D Materials, vol. 11, no. 3. IOP Publishing, p. 035025, May 30, 2024. https://doi.org/10.1088/2053-1583/ad4c73

Speaker: Dr Martin Gmitra (Institute of Physics, Pavol Jozef Šafárik University in Košice, 04001 Košice, Slovakia)

Dinner: FAREWELL DINNER

169 Folklore Ensemble Skadzi-Stadzi

Let us introduce ourselves to you in our current grouping. We, the members of FSk
Skadzi Stadzi, were in different periods of our lives part of the dance and singing component of FS Jánošík - Svit, FS Vagonár Stará škola, FSk Batizovce, folklore singing groups Východňarské Šarkanice, Jaščurečky and Slovenka Poprad. In September 2023 we separated into an independent artistic ensemble and we are working, among other things, on modifying performances according to the needs of the client in accordance with the observance of folk customs and traditions. The current ensemble of FSk Skadzi Stadzi is mainly dedicated to singing works in accordance with short dance choreographies and at the same time presents folk music of different regions of Slovakia by creating complete scenic bands in time lengths as requested. At present we present our work at cultural and social events and events within the Eastern Slovakia region. The repertoire consists of songs from different regions of Slovakia, customary bands of calendar ceremonial folklore and independent singing performances in alternative costumes, which we try to gradually add to the appropriate grouping of clothing to the region according to the financial possibilities. During the CSMAG '25 conference we will present a singing group of well-known songs from the Zemplín region and an emotional and joyful group in the Rusyn dialect.

Folklore singing and costumes in Zemplín

Zemplín, a region with a rich cultural tradition, is known for its distinctive folklore expression. Traditional singing in Zemplín is characterised by a distinctive melody, strong emotional expression and archaic elements that reflect the life of the rural population. The songs often accompany various life events - weddings, harvests or religious festivals - and retain a deep connection with nature and everyday life. Zemplín costumes are equally unique - colourful, richly decorated and varied according to the individual villages. Women's costumes often include embroidery with geometric and floral motifs, rich skirts and scarves, while men's costumes are simpler but dignified, with an emphasis on the shirt and belt. Each costume carries a symbolism that reflects the particular village, region, age or social status of the wearer. The presented costumes contain elements and style of Zemplín clothing - brightly coloured skirts and lajblik, ribbons, a cap with a scarf, an embroidered apron.

Ruthenian folklore, singing and costumes

The Ruthenians, an indigenous ethnic group living mainly in northeastern Slovakia, still preserve rich folklore traditions that are an important part of their cultural identity. Ruthenian folklore is distinguished by its authenticity and strong connection with nature and spiritual life. It includes folk dances, customs, fairy tales and, above all, singing.

Traditional Ruthenian singing is multi-voiced, often melancholic and characterized by a wide range and distinctive harmony. The songs accompany life events such as births, weddings, deaths, as well as everyday work and holidays. Spiritual and Church Slavonic songs are significant and form an important part of the Ruthenian liturgical heritage. Ruthenian costumes are varied according to individual villages and regions. Women's costumes tend to be rich in embroidery, lace and colourful ribbons, complete with scarves and aprons. Men's costumes are simpler, often decorated with leather belts and embroidered shirts. Each costume carries elements of tradition, social status and religious affiliation. The presented costumes contain elements and style of Ruthenian clothing - a blue-printed skirt, a white shirt, a cross scarf with tassels, a flowered scarf to cover the head.

It is a tradition in Slovak folklore that a woman, after going through the marriage ceremony, was grafted by married women, thus being admitted to the status of a married woman and assigned the duties of a married woman. A married woman had to wear a cap and a scarf, and her hair had to be hidden as a symbol that she was already taken and did not show her beauty. In many areas of Slovakia, this ceremony is still a tradition and part of wedding receptions. The man's feathers were removed from behind his hat or the colour of the ribbons on his hat was changed, which also depended on the particular region.

Speaker: Skadzi Stadzi

Fri, July 11

Section S10: Other magnetic materials and applications - PART 1

Convener: Jan Minar (University of West Bohemia, Plzen)

170 Spin-Wave Mediated Mutual Synchronization and Phase Tuning of Spin Hall Nano-Oscillators

Generation and manipulation of propagating spin waves (PSWs) in magnetic multilayer systems have opened new frontiers for magnonics and spin-wave-based computing [1]. The precise control of frequency and phase of PSWs in nanoscopic CMOS compatible systems is of high importance for emerging applications such as reservoir computing and Ising machines [1,2,3]. Recently, spin-orbit torques have been shown to drive PSW auto-scillations in perpendicular magnetic anisotropy (PMA)-based nano-constriction spin Hall nano-oscillators (SHNOs) [2]. Due to their long-range propagation, the mutual synchronization of SHNO, previously demonstrated in 1D chains [4] and 2D arrays [5], can also benefit from these PSWs.

In this work [6], we report spin-wave mediated variable-phase mutual synchronization in nano-constriction SHNOs, enabling both in-phase and anti-phase synchronization of their individual auto-oscillatory modes. Using W/CoFeB/MgO trilayers with PMA, SW auto-oscillations were observed and characterized via electrical measurements and phase-resolved micro-focused Brillouin light scattering ($\mu$-BLS) microscopy. Electrical power spectral density measurements on W/CoFeB/MgO samples with 500 nm spacing reveal distinct synchronization regimes, including constructive (in-phase) and destructive (anti-phase) interference patterns. These patterns (denoted as regions II and III) can be further controlled through the applied magnetic field and direct current. In contrast, in-plane magnetized W/NiFe systems showed no phase control due to the absence of PSWs. Phase-resolved $\mu$-BLS confirms both in-phase and out-of-phase states, providing conclusive evidence of long-range SW coupling. Micromagnetic simulations corroborate the experimental results and highlight the role of SW dispersion in phase tuning. Additionally, voltage-controlled magnetic anisotropy (VCMA) is proposed for localized phase control, offering a scalable mechanism for phase-tunable SHNO arrays. These findings hold significant promise for SW-based Ising machines, neuromorphic computing, and reconfigurable logic devices [1,3,6].

References

[1] A. V. Chumak et al.; IEEE Transactions on Magnetics, 2022, 58, 1. https://doi.org/10.1109/TMAG.2022.3149664
[2] H. Fulara et al.; Science Advances, 2020, 5, eaax846. https://doi.org/10.1126/sciadv.aax8467
[3] A. Litvinenko et al.; Communications Physics, 2023, 6, 227. https://doi.org/10.1038/s42005-023-01348-0
[4] A. Kumar et al.; Nano Letters, 2023, 23, 6720. https://doi.org/10.1021/acs.nanolett.3c02036
[5] M. Zahedinejad et al.; Nature Nanotechnology, 2020, 15, 47. https://doi.org/10.1038/s41565-019-0593-9
[6] A. Kumar et al.; Nature Physics, 2025, 21, 245-252. https://doi.org/10.1038/s41567-024-02728-1

Speaker: Dr Akash Kumar (Applied Spintronics Group, Department of Physics, University of Gothenburg)

171 Pt-Doped WS$_2$ the First Extrinsic Dilute Magnetic $2$D Semiconductor

Two-dimensional ($2$D) magnets have emerged as a promising platform for both fundamental studies of low-dimensional magnetism and the development of next-generation spintronic devices. However, intrinsic $2$D magnetic materials often suffer from low Curie temperatures, environmental instability, and limited tunability, posing significant challenges for practical device integration. To overcome these limitations, extrinsic dilute magnetic semiconductors (DMS) provide an alternative route to achieving robust magnetism in $2$D systems. In extrinsic DMS, a non-magnetic dopant interacts with a semiconducting host, inducing magnetic functionality without the need for intrinsic magnetic elements. This approach allows for precise control over atomic-scale interactions making them ideal platforms for investigating magnetic phenomena in $2$D materials. Here, we present the first realization of an extrinsic $2$D DMS in platinum-doped tungsten disulfide (Pt-WS$_2$). Using a bottom-up synthesis approach, we achieve a uniform and highly crystalline monolayer, where platinum selectively occupies the tungsten sub-lattice. The orbital hybridization between W $4d$ and Pt $5d$ orbitals leads to spin-selective states, resulting in a pronounced valley-Zeeman splitting. Our combined experimental and theoretical investigations reveal a sizable ferromagnetic response with a Curie temperature of approximately $375$ K. These findings demonstrate a novel strategy for engineering $2$D magnetism through atomic-level interaction design, paving the way for future advancements in spintronic devices, valleytronic applications, and magnetic nanoactuation.

Acknowledgements

This work was supported by the Taiwan National Science and Technology Council and Academia Sinica.

References

[1] Y. Chen et al., “Pt@WS2 ‐an Extrinsic 2D Dilute Ferromagnetic Semiconductor Beyond Room Temperature,” Small Methods, vol. 9, no. 3. Wiley, Sep. 20, 2024. https://doi.org/10.1002/smtd.202400955

Speaker: Ya-Ping Hsieh (Department of Physics, National Taiwan University)

172 Unmasking the Intrinsic Spin Dynamics at the Interfaces of $2$D Materials and Ferromagnets

The integration of two-dimensional ($2$D) materials into spintronic devices has long promised revolutionary improvements in performance and energy efficiency, yet progress has been hampered by interface contamination, oxidation-induced magnetic pinning, and compromised transmission at the $2$D/ferromagnetic (FM) junction. In our work, we introduce an advanced, single-step deposition process that simultaneously deposits asymmetric FM contacts onto atomically thin barriers such as graphene and molybdenum disulfide (MoS$_2$), thereby achieving pristine, ultra-clean interfaces.

Leveraging this novel fabrication method mediates oxidation and contamination effects and reveals the intrinsic response of the $2$D/FM junction. The resulting devices demonstrate exceptional magnetoresistance and significantly reduced coercivity, directly reflecting the inherent properties of the $2$D interface. We observe a novel metallization effect between MoS$_2$ and its contacts. The use of multilayer MoS$_2$ not only suppresses metallization effects but also restores semiconducting behavior, facilitating robust spin-filtering and yielding record-negative magnetoresistance values. Our advances underscore the critical importance of precise interface engineering in optimizing spin injection and magnetic anisotropy for the development of next-generation, $2$D spintronic devices.

Acknowledgements

This work was supported by the Taiwan National Science and Technology Council.

References

[1] T.-C. Huang et al., “Realizing High-Quality Interfaces in Two-Dimensional Material Spin Valves,” ACS Materials Letters, vol. 6, no. 1. American Chemical Society (ACS), pp. 94–99, Dec. 05, 2023. https://doi.org/10.1021/acsmaterialslett.3c01194

Speaker: Mario Hofmann (National Taiwan University)

173 Spin-Glass and Quantum Spin Liquid Ground-States in NaCdM$_2$F$_7$ Pyrochlore (M = Co$^{2+}$, Ni$^{2+}$, Cu$^{2+}$) and Defect-Fluorite (M = Mn$^{2+}$) Antiferromagnets

The family of $A^\prime A^{\prime\prime}B_2$F$_7$ pyrochlore fluoride antiferromagnets represents a unique but understudied class of materials containing the three-dimensional frustrated network of corner-sharing tetrahedra. While the rare-earth-based $A_2B_2$O$_7$ pyrochlore oxide counterparts have long been the main focus of study for their exotic magnetic ground states (spin glass, spin ice, spin liquid, order-by-disorder etc.), studies of these systems require extremely low temperatures due to the weak dipolar interactions between the magnetic $4f$ ions (|$θ_{CW}$| $\sim 10^0$ – $10^1$ K).

Conversely, the $A^{\prime}A^{\prime\prime}B_2$F$_7$ pyrochlore fluorides [1] overcome this limitation by replacing oxygen (O$^{2-}$) with fluorine (F$^{1-}$), enabling the stabilization of divalent magnetic $3d$-transition-metal ions (from Mn$^{2+}$ to Cu$^{2+}$) with stronger super-exchange interactions via F$^-$ ligands (|$θ_{CW}$| $\sim 10^1$ – $10^2$ K) on the pyrochlore $B$-site. Charge balancing and structure stability constraints, however, require a mixed occupancy of the pyrochlore $A$-site by monovalent A$^{\prime +}$ (Na$^+$) and divalent $A^{\prime\prime2+}$ (Ca$^{2+}$/Sr$^{2+}$/Cd$^{2+}$) cations, leading to chemical disorder. Consequently, this chemical mixing introduces magnetic bond disorder – local variations in the magnetic exchange energy $J$ - due to the $A^{\prime +}$/$A^{\prime\prime 2+}$ ionic size mismatch.

In our contribution, we report the successful synthesis and magnetic characterisation of novel frustrated NaCd$M_2$F$_7$ pyrochlore ($M$ = Co$^{2+}$, Ni$^{2+}$, Cu$^{2+}$) and defect-fluorite ($M$ = Mn$^{2+}$) antiferromagnets. [2,3] While $M$ = Co$^{2+}$ ($J_{eff} = 1/2$), Ni$^{2+}$ ($S = 1$) and Mn$^{2+}$ ($S = 5/2$) indicate a frozen spin-glass ground-state below $T_f\sim 2$ – $4$ K by means of AC susceptibility measurements, $M$ = Cu$^{2+}$ ($S = 1/2$) shows no magnetic transition in magnetisation (DC & AC) or specific heat, with continued spin dynamics down to $50$ mK confirmed by ${\rm \mu}$SR and NMR measurements. Furthermore, the power-law scaling of $\chi$($T$) and data collapse of $C_{mag}/T$ and $M$($H$) in NaCdCu$_2$F$_7$ hint at the realisation of a $S = 1/2$ random-singlet quantum spin liquid ground-state on the pyrochlore lattice [4].

References

[1] D. Reig-i-Plessis and A. M. Hallas, “Frustrated magnetism in fluoride and chalcogenide pyrochlore lattice materials,” Physical Review Materials, vol. 5, no. 3. American Physical Society (APS), Mar. 29, 2021. https://doi.org/10.1103/physrevmaterials.5.030301
[2] A. Kancko et al., “Structural and spin-glass properties of single crystal J eff = ½ pyrochlore antiferromagnet NaCdCo2F7: correlating T f with magnetic-bond-disorder,” Physica Scripta, vol. 98, no. 7. IOP Publishing, p. 075947, Jun. 29, 2023. https://doi.org/10.1088/1402-4896/acdeb7
[3] A. Kancko et al., “Spin-glass ground states in the frustrated pyrochlore and fluorite antiferromagnets NaCd$M_2$F$_7$ ($M$ = Ni$^{2+}$, Mn$^{2+}$),” 2024, arXiv. https://doi.org/10.48550/ARXIV.2411.11579
[4] I. Kimchi et al., “Scaling and data collapse from local moments in frustrated disordered quantum spin systems,” Nature Communications, vol. 9, no. 1. Springer Science and Business Media LLC, Oct. 22, 2018. https://doi.org/10.1038/s41467-018-06800-2

Speaker: Mr Andrej Kancko (Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University)

174 Magnetic Slip Casting: A Route to Realize Rotational MCE in Textured Polycrystals

Magnetocaloric cooling is being widely studied for its multifaceted applications such as magnetic refrigeration, liquefaction of gases, hyperthermia, etc. Magnetocaloric effect (MCE) involves the cooling/heating of a magnetic material under adiabatic magnetic field change. Rare-earth-based materials exhibit large MCE due to their inherently large magnetic moment but are not sustainable. Transition metals-based MCE materials are therefore gaining momentum and are being engineered in multiple ways to maximize the MCE.

Our work is centered on producing textured polycrystalline samples of transition metals-based alloys with a pronounced magnetocrystalline anisotropy. This will enable us to tap into the rotational magnetocaloric effect (RMCE) which would generate a larger magnetic entropy change than the traditional MCE. In this pursuit, we are using ‘Magnetic Slip Casting’ to synthesize textured polycrystals. The target alloy is prepared by arc melting or solid-state synthesis, post which it is subjected to ball milling to reduce the particle size. Using a suitable solvent like absolute ethanol and a stabilizing agent such as polyethylenimine, a stable slurry is prepared and casted into a silica tube mounted on an alumina support with a membrane filter. Over a few hours, the solvent dries up leaving behind a pellet. If this process is done in the presence of a small magnetic field, the crystals can be aligned along the magnetic easy axis, resulting in a crystallographically textured green body. This method requires tremendous optimization of several parameters like particle size, solvent-to-powder ratio, pH of the slurry, etc. However, this technique will be an effective process and has, so far, not been used to produce magnetocaloric materials.

We are focusing on Mn$_{x}$Fe$_{5-x}$Si$_{3}$ and (Mn,Fe)$_{2}$(P,Si) materials as they have strong magnetocrystalline anisotropy with an easy ab plane and an easy c-axis, respectively [1,2]. The textured sample when rotated in a constant magnetic field from its easy to hard direction, exhibits a sizeable magnetic entropy change. RMCE is generally observed in single crystals, which are tedious to grow, and mimicking the same effect by the proposed method will prove to be competent.

Acknowledgements

The project MagRota is funding by Normandy Region under the program « Normandie Recherche - Labels d'excellence» (n°23E06217)

References

[1] L. Caron et al., “Magnetocrystalline Anisotropy and the Magnetocaloric Effect in Fe$_2$P”, Physical Review B, vol. 88, no. 9. American Physical Society (APS), Sep. 30, 2013. https://doi.org/10.1103/physrevb.88.094440
[2] H. Yibole et al., “Magnetic properties, anisotropy parameters and magnetocaloric effect of flux grown MnFe4Si3 single crystal,” Journal of Magnetism and Magnetic Materials, vol. 504. Elsevier BV, p. 166597, Jun. 2020. https://doi.org/10.1016/j.jmmm.2020.166597

Speaker: Swathi Sakthivel (Laboratoire de Cristallographie et Sciences des Matériaux (CRISMAT))

10:30 AM Coffee break

Section S10: Other magnetic materials and applications - PART 2

Convener: Prof. Pavel Ripka (Czech Technical University, Faculty of Electrical Engineering)

175 Quantum Materials and Magnetic Phenomena Studied by Spin Resolved ARPES: Theoretical Perpectives

Quantum materials exhibit a complex interplay between electronic correlations, topology, and magnetism, placing them at the forefront of condensed matter physics and quantum technology. Understanding these systems requires disentangling spin-orbit coupling, electron-electron interactions, and magnetic fluctuations under realistic conditions, including finite temperatures and structural disorder. Spin- and time-resolved angle-resolved photoemission spectroscopy (STARPES) is a crucial technique for probing electronic and spin structures in magnetic and topological materials. However, quantitative interpretation of spin-ARPES data necessitates advanced theoretical models that accurately capture electronic states, spin textures, and dynamic responses to external fields.

I will present a theoretical framework based on the fully relativistic multiple-scattering Green function KKR method [1], effectively modeling spin-dependent photoemission. This approach includes correlation effects via dynamical mean-field theory (DMFT) [2] and describes spin fluctuations using the alloy analogy model [3]. I will also discuss advances in calculating light-induced electronic excitations [4], highlighting their relevance to spin-ARPES studies of topological and magnetic quantum materials.

A novel application is the one-step model of photoemission in studying altermagnets and kagome magnetic materials. Altermagnets, exhibiting unconventional time-reversal symmetry breaking without net magnetization, are explored in RuO$_2$ and MnTe [5,6]. Spin-ARPES combined with the one-step model provides insights into lifted Kramers spin degeneracy, revealing their potential for spintronics. In kagome magnetic materials, persistent flat band splitting and selective band renormalization are observed in FeSn thin films [7], highlighting unique correlation effects and topological phenomena. These developments offer a comprehensive framework for exploring magnetic phenomena and spin dynamics in complex quantum materials.

Acknowledgements

I would like to thank the Quantum Materials for Sustainable Technologies (QM4ST) project with Reg. No. CZ.02.01.01/00/22_008/0004572, cofunded by the ERDF as part of the MŠMT.

References

[1] H. Ebert et al., “Calculating condensed matter properties using the KKR-Green’s function method—recent developments and applications,” Reports on Progress in Physics, vol. 74, no. 9. IOP Publishing, p. 096501, 2011. https://doi.org/10.1088/0034-4885/74/9/096501
[2] J. Minár, “Correlation effects in transition metals and their alloys studied using the fully self-consistent KKR-based LSDA + DMFT scheme,” Journal of Physics: Condensed Matter, vol. 23, no. 25. IOP Publishing, p. 253201, Jun. 08, 2011. https://doi.org/10.1088/0953-8984/23/25/253201
[3] J. Minár et al., “One-step model of photoemission at finite temperatures: Spin fluctuations of Fe(001),” Physical Review B, vol. 102, no. 3. American Physical Society (APS), 2020. https://doi.org/10.1103/physrevb.102.035107
[4] J. Braun et al., “Correlation, temperature and disorder: Recent developments in the one-step description of angle-resolved photoemission,” Physics Reports, vol. 740. Elsevier BV, pp. 1–34, 2018. https://doi.org/10.1016/j.physrep.2018.02.007
[5] J. Krempaský et al., “Altermagnetic lifting of Kramers spin degeneracy,” Nature, vol. 626, no. 7999. Springer Science and Business Media LLC, pp. 517–522, 2024. https://doi.org/10.1038/s41586-023-06907-7
[6] O. Fedchenko et al., “Observation of time-reversal symmetry breaking in the band structure of altermagnetic RuO 2,” Science Advances, vol. 10, no. 5. American Association for the Advancement of Science (AAAS), 2024. https://doi.org/10.1126/sciadv.adj4883
[7] Z. Ren et al., “Persistent flat band splitting and strong selective band renormalization in a kagome magnet thin film,” Nature Communications, vol. 15, no. 1. Springer Science and Business Media LLC, 2024. https://doi.org/10.1038/s41467-024-53722-3

Speaker: Jan Minar (University of West Bohemia, Plzen)

176 Technogenic Particles Emission Sources Identification with Magnetic Methods and Mössbauer Spectrometry

The aim of the study was to characterize, using Mössbauer spectrometry and magnetic analysis, the technogenic magnetic particles (TMPs) from non-ferrous metallurgy, cement, coke, glass production as well as long-range transport (LRT) [1] and compare the obtained data with previous results focused on iron mining and metallurgy [2]. The basic magnetic parameters used for TMPs characterization are magnetic susceptibility, saturation magnetization, remnant magnetization after saturation, standard coercivity, and coercivity of remanence. The Mössbauer spectrometry provides additional characteristics like hyperfine magnetic fields, quadrupole splitting, isomer shift, percentage of iron-bearing phases and stoichiometry parameter of magnetite.

The main characteristics of TMPs produced by Fe mining are: high values of concentration-dependent magnetic parameters, low values of coercivity, a significant contribution from coarse grains and a relatively high stoichiometry of magnetite. The most discriminative feature for TMPs generated by the glass industry is the abundance of goethite in the topsoil samples. The TMPs released by the Ni-Cu smelter and the Pb-Zn waste exhibit significant differences in the Mössbauer parameters, indicating different stoichiometry of magnetite for each group. Such variations are due to the replacement of Fe by other elements at tetrahedral sites in the case of TMPs released from the Ni-Cu smelter. The magnetic features of TMPs from cement production depend on the applied technology. TMPs characteristic for the LRT emissions contain a higher amount of finer fraction of low stoichiometry magnetite strong influence of the local pollution.

Acknowledgements

The study was partially funded by the National Science Center of Poland (project n° 2016/23/B/ST10/02814). Special thanks to Prof. Tadeusz Magiera, Prof. Beata Górka-Kostrubiec and Dr Michał S. Bućko for very fruitful work on the project.

References

[1] T. Magiera et al., “Technogenic magnetic particles in topsoil: Characteristic features for different emission sources,” Science of The Total Environment, vol. 865. Elsevier BV, p. 161186, Mar. 2023. https://doi.org/10.1016/j.scitotenv.2022.161186
[2] T. Magiera et al., “Technogenic magnetic particles from steel metallurgy and iron mining in topsoil: Indicative characteristic by magnetic parameters and Mössbauer spectra,” Science of The Total Environment, vol. 775. Elsevier BV, p. 145605, Jun. 2021. https://doi.org/10.1016/j.scitotenv.2021.145605

Speaker: Tadeusz Szumiata (Department of Physics, Faculty of Mechanical Engineering, Casimir Pulaski Radom University)

177 Exploring the Soft Magnetic Properties of Various Iron-Silicon Alloys Manufactured via Selective Laser Melting

The combination of the increasing use of additive technologies and the availability of advanced materials allows for further efficiency improvements in existing applications and more sustainable solutions. The widespread use of silicon steels opens up many areas of development for engineers working in more depth with additive technology.

In this study, the $3$D printing applications of four different iron-silicon alloys (Fe-$6.5$wt$\%$Si, Fe-$6.9$wt$\%$Si, FeSiB, and gradient FeSi) were investigated. The materials were prepared by gas atomization and mechanical grinding, with the samples being prepared by selective laser melting (SLM). The effects of several printing parameters, such as print orientation, volumetric energy density (VED), and table temperature, were investigated. The samples produced were toroidal and sheet metal plate samples, on which the complex magnetic permeability spectrum and DC hysteresis curve were investigated. Due to the unique microstructure and crystal structure of the printed samples, optical and scanning electron microscopy (SEM) studies, as well as computed tomography (CT) measurements, were performed to investigate their porosity.

The comparison shows that materials that cannot be machined by other technologies can be printed in complex geometries and large sizes. By fine-tuning the SLM printing parameters, these materials can be tailored to the specific application.

Speaker: Bence Kocsis (University of Szeged)

178 Strain Induced Martensite in the Austenitic Steels and its Monitoring via Barkhausen Noise Emission

This work is focused on the implementation of Barkhausen noise technique for monitoring of phase transformations in the austenitic steel after plastic deformation under the variety of loading regimes. The non-ferromagnetic austenite is transformed into the ferromagnetic martensite. The depth extent as well as the specific character of this transformation can be reliably monitored via Barkhausen noise emission. The work present the result of experimental studies focused on the rolling wear, shot peening as well as more complicated regimes of the load in the real long term conditions. This presentation demonstrates the significance of the mutual communication among the neighboring martensitic islands as well as the preferential straining of the parental matrix during some regimes of the load. Barkhausen noise can be therefore employed for very fast, reliable a non-destructive monitoring of the aforementioned processes.

Speaker: Miroslav Neslušan (Faculty of Mechanical Engineering, University of Žilina)

12:30 PM CSMAG'25 - Closing Address

1:00 PM LUNCH